owned them both mate owned a 96 M3 evo 321bhp and a 01 impreza P1, 276bhp ish, these I guess are similar comparisons to what your asking although my m3 has what 40bhp more than the older one your talking about and the sti doesnt come close to the P1.

buy the scooby if you want all weather performance

buy the M3 if you want, class, reliability, and tail happy performance, these are dangerous in the winter