Did a ride in some F-15's a while back, as kind of an exchange thing. I was a tanker guy at the time, and the fighter guy I was working with offered me a ride. We went up and did 3 sorties of 1 vs. 1 BFM (basic fighter maneuvering, aka dogfights) and pulled a whole lot of 8.5 g turns whenever we were defensive. Basically about 30 seconds per pull.
Basically the g-suit gives you about a 1g advantage over what you would have normally, but the real advantage of it is that it reminds you to SQUEEZE your legs and butt muscles. It helps, but the real help is to remind you to perform your anti-G strain manuever (AGSM)
The other thing to remember is that your body gets acclimated to the g's. When I first got back into the T-37 as an instructor, I had to start my AGSM at about 3-4 g's, and now I start straining around 5g's on most days. That's without a G-suit.