If we look in the rule books for the Grand AM cup and the USTCC. They put retarded weight restrictions on similarly powered AWD vehicles.
When a Subaru Wagon with a totally stock powertrain from intake to exhaust weighing 3100 lbs gives a Mazda RX8 weighing 2650 lbs a run for the money around the track there must be some advantage…
http://www.grand-am.com/CONTENT/Docs/PDF/2006/Tech%20Bull%202006-06.pdf