well.. the 5 speed isn't bomb proof either so..

S15 engine is low port, the SR20 guys generally prefer a high port design. the S15 engine is going to cost you in the range of $5000 too. at least twice as much as a S13 engine. with the S15 engine you can make more HP on the stock turbo though so things kinda go both ways with this decision. the S15 comes stock with a T28 as apposed to the T25 found on the S13 models.

when I get my SR20 I will get a s14 model. its a 5 speed, which is a proven tranny (at least I know whats going to break, with the 6 speed you may have a harder time replacing broken parts, and it would be very expensive) and it also comes with a T28, its newer which ='s less milage. it also has the VTC that the S15 has been praised for having. it can be sourced from 94-98 silvias and puts out 217HP stock as apposed to the 202HP on the S13.

S14... newer then S13, less milage, bigger turbo, cheaper to fix tranny if you break it.

by the way. the S15 may have more HP factory but the S13 and S14 engine make 203 ft-lb of torque as compared to the S15 which makes 202.

oh, and... you could import a whole S15 silvia to the US right now. but it would have to be for off road use only. you would never be able to register the car. unless you were filthy rich and it was your dying goal. .you'd probably have to crash test a couple of them like motorex did the skyline.