My Exedy OEM (RS version) holds my 300+hp nicely, I don't beat my car though... The WRX version is said to hold over 400..
Don't bother with a LWFW... really.. There's as much bad said about them as good.. I run one, it came with the car.. my car's also modded in most ways, besides internals..
You should do the rear main and the block off plate while you are in there..
To many it's easier to pull the motor than drop the trans... dropping it is the easy part, putting it back and getting it lined up, while trying to keep blood in your arms and not dropping it on your head is the hard part..