I needed to replace the tyres when I bought my 350z and went with Kumho PS71 which were just over £400 fitted. I've done about 4000 miles and 4 track days on them (2 of them wet days) but personally I'm very happy with them, I think they provided great grip on them days, the current road conditions, and wear seems to be very good with plenty of life left. So I'll probably buy them again when the time comes!
I did look at PS4 but decided that the £200 odd difference was better spent on good pads and brake fluid so I didn't have any issues on track. As others have said you don't want to forget about things like Alignment, worn bushings, brakes, etc. Personally the last thing I would want to do is put expensive tyres on and the car still feel terrible/ tyres not last as the alignment is out or bushings are worn