yeah i had a similar battle when i was purchasing my z. i've driven my friend's 335, and while i enjoyed it, it didn't give me that sports car feeling. imo, the z is more fun to drive. as far as the oil issue goes, i dont track my car (yet), but in my "spirited" driving that i do, i haven't seen any oil temp issues. we'll see how that goes during the warmer seasons in TX.
if practicality is an issue, then definitely go with the 335. be forwarned about issues with the 335 though. my friend's 335 has had to get the fuel pump replaced, along with the fuel injectors. it was covered under warranty, but that's a pain. once the unlimited warranty dries up, the maintenance will be $$, but since you already have a few beemers, you know that