There are better tyres around than the PZero Nero. The Michelin PSS is clearly a superior tyre performance wise (possibly outperforming the car...). It's also priced at a premium generally and anecdotally wears faster. My compromise was to consider PS3s (so nearly bought these). I've had Continental CSC3 and CSC5 on other cars -- the former were often fitted new to the Ti and my experiences with both have been excellent.
Goodyear Eagle F1 Asymmetric 2 is another OEM choice for the Ti. I can't recommend them highly enough. I was offered 245/35 but the sidewalls are narrow enough already for mine.
As for the 245/40 fitment, as per this thread there is no reason not to fit them. I think I actually prefer them!
Now -- as it happens I did happen to put a dent in my rear wheelarch and the metal DID foul on the sidewall (just). Possibly would have happened with 235s anyway... I reached under and pulled it out. No issue. And now fixed!!
I'll post a photo so you can make up your own mind about the aesthetic. Remember we are talking 10mm of tread and about 3mm of additional diameter.

[EDIT: Photobucket is playing up so PM me your email Colin and I can send you more. The tyre does not extend beyond the metal.]
After much research I'm very happy with my 245s and I wouldn't pay any extra for 235s.