I had a 750, best bike I ever owned. It’s basically the body and weight of the 600 with power closer to a 1000. Best of both worlds IMO since the 1000s are heavier.
I mean 600s are fine too but so much shifting haha. I could ride on the highway at cruising speed in second gear just under my power band so I could slightly flick my wrist to pass people. Amazing feeling.
Also was fantastic at the track. I also rode an R6 at the track and the amount of shifting I had to do was annoying compared to the 750 where I could mostly focus on my lines.
Anyway TL;DR the GSXR750 is awesome and you should get it. I can’t think of any good reason to get the 600 when the 750 exists unless you’re racing in the 600 class or something and can’t go higher due to the rules.