I have a first-flight '98 DOHC 2.5RS, with the well known problem of From-the-Factory-Clutch-Shudder-From-Hades.
After the usual run around with the dealer, i ended up buying the subaru-replacement flywheel (the old 98 flywheel has of course been superceeded with a new part), and had a specialty shop (NOT your average run of the mill machine shop) cut the replacement from 22.1 lbs to 15.6 lbs. There is a grunch of excess metal on the backside surface, and it left a large margin of safety after machining and balancing. Throttle response is only SLIGHTLY improved, and shifting was noticably improved (suspect faster flywheel spin-down during shift into next gear...)
Without the turbo, it's really not (IMHO!) worth the effort. The 2.5 has the low-end to deal with a slightly heavy flywheel, and there is a definate degredation of idle-smoothness (gee, imagine that.) There are aluminium f/w's under 10 lbs, *I* can't even begin to see that as a streetable, everyday-driver f/w. It would be unreasonable to be doing 4k clutch drops from every stop sign, just to keep the motor going. I'm sure for RACING/RALLY, it's a great idea.
My final pressure plate ended up being a custom-created 1850 lb. dual-diaphram (using subaru original carrier), with a 9-pad copper/ceramic disc (not a puck, guys. a disc :-)).
I had a TERRIBLE experience with the Unorthodox kevlar clutch/pressure plate... the p/p and (original at the time) flywheel were properly machined, and bed-in procedures were strictly followed. It's too bad that the p/p was only 1125 lbs (STOCK was 1280) and the clutch wouldn't lock up under the power of an UNmodified motor (much less the turbo). After 10k miles of "oh, it's just bedding in", i took it out, to discover that the disc carrier had cracked in 4 places, and the p/p and f/w were HORRIBLY heat-scarred.
The copper/ceramic pad clutch locks up first time, every time, under the most horrible launches. Even under extreme heat - multiple, rapid launches for ex, - the disc still locks hard. I have the quaife (torsen-style) rear differential, and I have NO problems getting the wheels to unlock on pavement from a launch (don't try this at home kids, I'm GENTLE on it, really.)
Anyway, the whole combo still shudders, but no worse than the stock setup, and will take double the torque from the motor :-)