M3 97-98 vs 99

Hello. I'm in the market for a M3. My delima is the 4-door sedans of 97-98, or a '99. I am bascially wondering, what is the diffrence b/t these model years? Mostly intrested in the diff. b/t the 98 and '99 models. Also, I've read about the M3 Evoloution, but I'm confused, was that a one time thing, and all the M3's from then on had the same "upgrades" the evolution had? Like the 3.2L engine? I just haven't found a good "history" on the M3's about the specific diff. b/t the model years. Only the just from 95-96 to 97-98. I also know the '99 has a "M" pacakge that gives those rainbow seats and the new seteering wheel. Is the '99 steering wheel avaliable on the '98? I really want a 4-door sedan, but I'm just checking in case there's a reason I should look at a '99, which only comes in a 2-door though. Thanks.