Personally I couldn't stand driving a Mustang with a V-6, that lovely straight six sound and smoothness is a big part of the BMW appeal to me. But that may be just me.
IRS is good, too - are any of the mustangs *not* live axle?
Personally I don't think that driving a 330 would be "settling" in any way. My ex has a E46 330xi and I think it's a great little car. If she hadn't bought it I probably would have bought it myself. But I ended up with a E92 335i instead, poor me