03/04Cobra uses the M112, Roush uses an M90 on these. There are lots of upgrades to squeeze more power out of them, though. Roush offers the TVS blower upgrade as well (similar to what was standard on the 510 hp P-51A/B models in '08 and '09). That upgrade will put you far beyond what your STi was doing if you have the bottom end that can take the beating.
1998 Roush: M112'd Aluminum block 4.6L 2V 6 speed track car
1999 SVT: Mostly stockish
1970 Mach 1: Resto-modded monster
2000 Roush #5004 - World's FIRST M112'd V6 Mustang. Sold, but not forgotten.