If you're keeping the M3, IMHO you'd have more fun going for something that offered more of a difference in driving experience: Cayman or 911 of some sort, Corvette or muscle car, or even a Subaru BRZ. Drove the BRZ recently and honestly in some ways liked it more than my M3; it's way down on power (though that should be fixed with FI soon enough), but it felt so perfect in the turns that I just didn't care -- plus weighing A THOUSAND POUNDS LESS than the M3 helps. Could be turned into a very capable track car relatively cheaply, probably with a total cost less than a new RS5.
Anyway, better to have two different experiences in two different cars than two similar cars. That's my 0.02.
Last edited by jphughan; 11-05-2012 at 05:33 PM.