Driven one on road and track. Road was a coupe manual, track was an SMG ragtop.
The interior looks dated, but is made of good quality stuff. I'd say it's an equal for a 350Z, rather than just better.
The engine is a peach, loves to rev and makes a great noise. Needs a good intake though!
M3 felt much heavier than the Zed, although I found it much easier to slide perversely. No idea why.
Brakes are sh*t and need upgrading. Seriously, you'll kill them far too easily as stock.
SMG 'box takes some getting used to, but I do quite like it. However, big bills when they go wrong as my mate with the ragtop has found out...
It just feels a bit big to be a sports car, but if you're happy with the BMW now then that's not a problem. I wouldn't say it felt significantly better on the turn in than a Zed, if at all.
645s are also available in the manual, but that's proper barging!