Most of the JDM sti motors are the same. 2.0l and high revving. USDM sti motors are 2.5l and rev to 7k. I personally like the bigger displacement for the higher torque. You could always build your heads to rev high later on down the road. OR with the JDM sti motors you could change out to a usdm sti shortblock to rev high on a 2.5l.

Or if you had the time you could swap out the shortblock on your RS and do a custom turbo kit. Waaaaaaay cheaper than a swap. You can just buy stock wrx/sti pieces that'll bolt right up to turbo your car. And a 2.5l sti block to make sure nothing breaks. Voila! One word of advice.....no matter what you do.....change out your tranny first....RS trannies do not hold up to too much torque especially if you race