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In regards to the original post. I have sharpened for customers at 20, 17 and 15 degrees primarily.  I now sharpen pretty much any decent kitchen  knife to 15 degrees... They always come back to me needing sharpened.  That's to say, I can't tell if one angle held up better or not. 
All but the cheapest steel should be stable at 15%.  Wootz or Larin showed the sharper the knife is, the longer it stays sharp.  The geometry allows a sharper edge at 15°.

 In the grand scheme of things, it doesn't matter. 90% of your customers won't know or care what angle they are sharpened to.

Yep, what he said...

As I re-read through all the comments there are a couple things that jump out.
First, many don't see the need or use for a Bess Tester.  I use mine for testing my work but more importantly,  I use it to learn new techniques and improve my current techniques. It is especially useful in the learning stages to see the way different steels and tempers react to being honed.
Secondly, I use it to confirm I have fully refined the tip, belly and heel. It will also show you when you've stropped too much.

In regards to the OP, the Bess enables you to learn what works and what doesn't. Under 100 is very realistic with the SG-250, depending on the steel. As some have mentioned, cheap steel sometimes just won't get under 120 for a variety of reasons.

Some folks see it as a way to compare results to someone else... I could care less.  Just trying to improve my craft, in my mind.

It is a useful tool for me, and has a premium spot on my bench.

I have found that it is much easier to get low BESS scores when I sharpen at low angles (sub-15 dps). In my experience diamond stones tend to produce lower scores than the SG-250, and higher grit finishes (1000+) produce lower scores than lower grit finishes.

Just to make sure : when you talk about lower scores, do you mean lower BESS number or lower sharpness ?

I meant lower BESS scores.

To rephrase, I've noticed that the SE-250 (extra fine diamond wheel) gives me lower BESS scores (sharper edge) than the SG-250 (standard stone wheel), on the same kitchen knife (Spyderco MBS-26 steel similar to VG10), at the same angle, using the same technique.

I have not experimented enough to say this is definitive. At the moment I suspect it could be due to grit differences, or that one abrasive cuts a certain steel cleaner than the other, or something else?

That is going deep into the weeds... Take it as one data point from "a guy in his garage seeing a thing". 🙂

In Vadim's book he does state there is a correlation between grit size and low BESS numbers.

I am a dedicated BESS user.  I use it several times on quality steel knives as I sharpen them.  It always removes the question of "how sharp" they are or if the burr has been fully removed. It is invaluable in determining how much and what technique to use stropping.

One last point... many have stated there is no point in striving for 50 bess.  The sharper a knife starts, the longer it stays sharp.  And, it's not liner.

Yes, you can sharpen under 100 with an SG wheel.  CBN or Diamond is more consistent.

Lastly, Bess testing will shave time off your honing learning curve. (If your taking notes).
IMHO

As an experienced user I imagine you have, but have you used a diamond plate to de-glaze and redress your stone?  I use cheap diamond plates in an 80 and 400 grit.  Allegedly the 80 will get the stone to 220 grit, the 400 comes out as 1000 grit.
It only takes a short time to deglaze or change the grit. 
I use the diamond truing tool as needed.

The 1200 grit CBN wheel will most certainly grind an initial edge on ceramic knives, but that edge will be completely unusable due to chipping (even with careful use)
For most commercial work after creating an initial edge on the SB-250 Blackstone i refine on a first Paper Wheel with 15 micron diamond compound (edge is still unusable after this), and then at least up to 6 micron diamond compound on a second Paper Wheel.
When there are no large chips i often only use the 15 and 6 micron Paper Wheels.

Further refinement with 3 micron diamond compound on a third Paper Wheel or even 1 micron diamond compound on a fourth Paper Wheel leads to a noticeable keener edge as well as much longer edge longevity.
The problem is of course that this also takes much more time, so after a lot of experimenting & testing i have found refinement up to 6 micron to be a good balance of edge keenness & longevity, and time spent sharpening/polishing.

Also: i avoid working on cheap ceramic knives, these are not worth it.
These days i only do quality ceramics.

Maybe this older thread is also helpful:

https://forum.tormek.com/index.php/topic,5672.0.html

Thank's for the intel...

Led light panels are relatively cheap, easy to install, bright and many you can change the color on.  The more the merrier.  Install more than you think you will need.  Never too much light in the workspace.

I'm wondering if anyone has duplicated these amazing results?
Inquiring minds want to know...

I have an old Gerber with a ceramic blade I would like to try on my T8. My question is, I have CBN wheels up to 1200.  Is that grit small enough or will chipping be an issue?

For me, edge leading gives me the water bump that helps me keep things square.
Edge trailing for hand sharpening for sure.

Maybe, instead of mold, the white fluff is efflorescence?

That is interesting, we have a water softener here and it's possible that it's related. 

This gets my vote.

It might just be salt then. Have you tasted it?

I'm joking but you can smear/crush a bit between your fingers, if it turns into chalky dust it is probably just salt/mineral build up.

Hi,

I seem to have some mold growing in and on the wheel, thinking I need to run a solution of hydrogen peroxide through the wheel to kill all of it.  Any idea whether this will harm the wheel?  Seems like a vitrified bond abrasive which should be chemically invincible I'd imagine.

I don't know the cause, but my wheel does the same.  Occasionally I don't use my SG for a couple weeks.  As it starts to dry it grows a little white fuzz.  It hasn't seem to make any difference.

Unlike yourself, I started with a belt grinder.  I use mine quite frequently for different needs when sharpening.  I have a 1x30 variable speed Rikon, but there are a ton of different units out there.  They can be pretty inexpensive and would quickly deal with that particular issue you're having.
If you're just sharpening your own knives it may be overkill , but you will find other uses as well.

I have encountered a similar issue about keeping the blade flat on the stone. The blade holder keeps hitting the post of the threaded part of the universal support bar. I am unable to slide the blade holder smoothly along the bar. What should I do to avoid this?

I believe I have been experiencing the same issue (occasionally) as you.  I believe the root cause is the KJ-45 jig.  Is that what you're using?
The collar on that style jig is a tad more than 90° to the USB.  It is flared out a bit causing that.
Someone had a similar issue and just filed off the area it was bumping on the USB support bar.  I will be doing mine in the morning.

My son printed my one a couple years ago, prior to that I made one out of wood ( both designs can be found on hackaday.com.
Recently I bought a cheap one off Amazon.  All of them work about the same.  Good enough.
Good luck with your design though.  I use a goniometer often and believe they are a staple in my tiny little shop.