First off, use the heaviest buffer you can for supers. I have one of the solid steel 7oz ones. (eg a 9mm buffer).
Start 20% under manual and work the load up. With the pistol length and lots of gas, you may be limited how much pressure you can run and still get the rounds to reliably extract. Expect stuck cases and such. That will tell you your upper limits.
I am a machinist, so I could easily make any kind of buffer I want - thanks for that suggestion!
Yeah, I know - I need to get/make an adjustable block - it's just that I have a real low profile one to fit under the handguard, need to find one that fits......