the m3 is a bit better ballanced (weight ratio), handles a lot better, and has much better breaks than the 325, i've seen turbo'd m's and 325's and even a 328 and talked to owners of all of them, many of the guys that had started with non m's said they wished they had in the long run, as for the year and obd set up everyone i've talked to about them thinks is the best bmw to turbo is the 95 M3's obd1. with the obd2 they usualy convert them to obd1 before turboing b/c of tuning and flow issues with the obd2 set up also with the 95s your supose to be able to run more boost on stock internals than with the obd2 cars (not sure why exacty)
dado on dtmpower.net has had two turbo's m3's here's a link to a page of info about his current car http://www.dtmpower.net/forum/showth...hreadid=110353
lets you know if your goin to go all out what all your goin to need
hope that helps
-riggs