I tried the m3 last year at willow springs and donnington and it was about on par with the Aston after I spent a while changing from the default setting
I have a decent tune on it now, in many corners I can easily go full throttle before the apex on Dubai International, but looks like I'm not going to get in the 41s (best so far was a 42.5xx). I'm surprised how good the M3 and GT4 cars feel driving wise, if more would've driven them online, I think it would be more fun than the GT3 class.I think the m3 likes to under steer on turn in if I remember. If you can dial that out and make it a bit more lively it comes alive.
It's taken me a long time to tune in any of these gt4 cars, I think they are by default slow and cumbersome, but with a little work you knock at least half a second off that time.