I had an S2k GT with hardtop a few years back, worst car I ever owned. Seats were so hard and such a limited range it adjust them, everything was cheap plastic inside and I ended up taking the hardtop off as all it did was rattle, drove
me mad. That was a low miler with FHSH.
Performance was totally different, very revvy and you had to rev the bits off it to get anywhere with it, was so disappointed in that car for what they build it up to be, sold it after 2 months as it did my back in.
The 350 is nice and torquey, much better build quality imho with all the toys as standard on a GT. Definitely try and test drive a couple of each car and make your mind up as they are so different honestly.
Plenty of nice 350z's around for your budget, have a good look and take your time to find the one you want. As you say, service history is very important on any of these types of car, not necessarily full dealer but at least a good history with quality parts used and things like brake fluid and gear box oil changes, tyres are expensive as I am sure you know!