95 US M3 cams would have the best cost to performance ratio because there are a lot of people removing their stock ones for aftermarket ones. Your car still remains very reliable and drivable. I don't know if the euro M3 cams would fit into the 325 head.
There are a bunch of companies selling aftermarket cams though, one of the best would be Schrick, but they are pricey.
"Driving is like a narcotic, an addiction that can take over lives. It ruins people, breaks families apart, and even kills. Itís habit that needs to be fueled. Time, money, rationality, sweat, knuckle skin, and anyone who disapproves are of little importance to a driver, and are often overlooked. Hi, Iím Nelson, and Iím a drivaholic."