Those SVXs are cool... one of my college buddies had one that he put an STi 6 speed in. I don't think he owns it anymore.
The older 5 speeds are kind of crappy though (I used to own an 02 WRX myself) the housing around the clutch would wear out and you'd get that "juddering" when starting out from a stop on wet or cold days, then of course the 1st gear synchros would wear out really fast so you'd have to double clutch if you ever wanted to downshift into first.
All problems with the subaru 5 speeds since the mid 90s. I don't think they fixed the design until the 04 models when they migrated to the same "butterfly" synchros and clutch housing design of the 6 speed.
of course the 6 speed wasn't without it's flaws either, nor was the clutch... but if you're going to go through the trouble of swapping out the transmission it's worth spending a little extra coin on an improved aftermarket clutch IMO.