a lot of guys when running lower numbers, like 350 and below (perhaps more, but few bikes to look from above that) just use stock clutch with heavy duty springs. that 2 piece clutch cam (stock part) acts as a lockup under heavy loads, the harder the accel, the harder the clutch holds together. but yeah, most guys go to a lockup and there are a few boost compensated ones floating around.... seems to be a lot of interest in them, but somewhat hard to get ahold of... as far as lowering and stretching, there is also a point were stretching it too much will hurt you because there wont be enough weight over the tire for it to have traction.
most unintercooled guys run 6-8 psi, and a few have gotten away with 10psi on stock compression. but most like to lower compression before going to 10psi. on an intercooled setup, though, guys are able to run more boost safely than without, obviously. i thnk lowered comp and intercooler guy have gotten lik 18psi n pump, but i havent heard as much about these due to them not being as common. but they are able to get 350hp on pump without problems it seems. even heard of a 400hp one on pump, but i think that there was some special stuff going on there.
but yeah, setup first gear for like 6psi, 2nd for 8psi, 3rd for 10, 4th for 12, 5th for 14, 6th for 16psi..... you know, something like that. that might be a little light on power in the lower gears, but you get the idea. mine at 4psi on stock compression thus far has proved to be difficult to keep the tire from spinning or wheelieing, but thats all in the fun IMHO