if you have the money go with the gsr, bec later down the road if u go with a b20 youll have to bore out resleeve and much more and hope you dont throw a rod bec of to high of comp. gsr you can boost on stock internals with no problem(as long as you dont put to much boost on it, which is 11 psi)

and even if you dont go boost, the gsr has a much higher red line, more stock WHP, and is a more dependable motor.
if you got the b20 to get and power out of it really is to make it a b20 VTEC, which is a pain in the ass! you would have to find the conversion head gasket, the right head studs, etc. and not to mention, with the b20 you would have to put a tranny on it, swap the head,(and if u didnt swap the head you would atleast have to find the correct intake mani.) and put the motor in the car.

with the gsr t would just be swap, wire up VTEC and whatnot, and go

so imho do the gsr