Tuned OS Giken options

I picked up some 3.63 gears and figure while I have it apart I should put a diff in while I'm at it.
Car is primarily autocross(run in XB), with a trackday or street driving occasionally. I don't really care about streetability, I'll deal with whatever is best for the parking lot races.

I've seen 2 different tuned options for the OS Giken, Supermiata/949 and Shaftworks. Anybody have experience with either of these or another option? I'm not really up on the specifics of what goes into tuning them just want what works for my application.

Car : 99 Miata, 305hp/260tq, 9LR aero, will be on 275 200tw, hoping to get to 2100ish lbs