45k is serious cash Gibbo.
I mean, you need to really, really consider what you go for here. Not that you wouldn't, but even more so. You may never find yourself lucky enough to do this sort of sized purchase again, so based on that... I'd be doing the following.
Ruling out performance audi's/bmw's. It's clear from many members on here that you can get older M3's/M5's and run them absolutely no problem when paying significantly less than your budget. Based on that, I'd 'miss out on the specialty' of having a newer/less owner/less miles/whatever version and pip for something seriously special.
Personally it would be out of 2 cars. An NSX-R (if 45k is enough) or a 911 of some sort.
An NSX-R whilst not many peoples cup of tea is, unquestionably, seriously unique. OK, its hillarious money for a Honda that looks like the 80's even in the NA2 revision, but it is a real head turning car. Before I moved to Watford in 2007 I'd only ever seen 1, after that point, I saw a further 3 cars (1 I was parked next to in a carpark which I ended up chatting to the owner to, she had owned it since new, 1 was owned by the parts manager at the Honda Garage I used, and the other I would see from time to time in central london.) Based on the way I know you drive, your the kind of person who could bring the best from an NSX and have incredible fun on the track with one. However, I do accept there are A LOT of people who would think it madness to spend this much money on a Honda.
Regarding the 911, I actually think its quite a tough one to work out which one I would have. Part of me would love a pre 89 Classic, but 45k is a lot of cash to spend on one of these. The other part of me would want the best 997 I could get (C2S/C4S for this money?).
In honesty mate, I think this is a tough one to do a thread on. This must be a special to you purchase. In my eyes I'd even consider something older like a 355 Ferrari, and use some of the change for a daily driver like a 1k Merc/Mondeo/Whatever but I dont know how open to this you are.
Best of luck with whatever you decide to go for