I did a 2013 M3 and modded it to 650 HP and also picked up a 2013 STi. But the alternative wouldn't have been an M5...it was a GTR or two year old 911T. Glad I did as the M3 has proved to be a GTR and 911T killer.
The M3 and M5 are two totally different cars. I don't think many people would cross shop these.
Daily: 2013 e92 M3 MW FR DCT ZCP / ESS VT2 650 S/C, MRF mid/Akra slip, ST BBK
Track/Airstrip: 2011 997.2 Turbo S PDK / GIAC tuned / Ohlins coils+LCAs+endlinks setup by BBI Autosport
Beater: 2013 X5 3.5sport