There is zero comparison in any respect. Zero. I owned two G37S coupes before my 2 E92 M3's. The G37S would lose to a stock 335i on the track, let alone an M3. Just get some laptimes online to confirm and show the huge spread. Here's one comparision... M3 vs. G37S Fastlaps
It is 7 seconds faster on a 1:35 track. That is MORE than a lifetime in the difference!!!
If it were me, I wouldn't even debate it with him because it is just a ridiculous assertion.