just go for the ///M and don't look back
I sold my Z4 coupe and replaced it with an M3
I test drove a 335, S4, S5, C63, and ISF
C63 was fastest in straight line no doubt
335i coupe was fun but felt bland compared to the M3
S4 and S5 were disappointments. I didn't feel connected at all with the S5, and the clutch was way too soft.
As far as the M3 being an inferior car to a mildly tuned 335...i'm not getting into that argument.
Thread starter: If you have a chance to sell the 335 and can afford the M3, I say go for it. But I wouldn't put myself into a bad financial situation. M3 will be a lot more expensive to maintain. You're looking at about 16-18mpg avg.