Setup matters, but not nearly as much as driving style, drafting and throttle input.
I'm trying to remember back, and I think in the GVS race with maxed out ZR1 RM's, the most I could do competitively was 10 laps, but 9 laps was faster in the long run for total time. I do believe I've made 20 laps in an Enzo before, but the guy who pitted at lap 10 was right on my butt by lap 19, meaning pitting is faster.
Regardless the trick to making tires last, is 80% throttle control in my opinion. Find a car with a solid pace, and just follow them. Let off the gas 50 feet before your normal braking point, and coast into the corner. Only apply 50-70% brake pressure, coast through the turn and then slowly accelerate out of the turn. I usually don't go full throttle until 3rd gear (based on tranny settings) Stay in the draft of the car ahead of you, and maintain the same speed they are, with about 80% throttle input. Do this for how ever many laps needed. This strategy allows you to go the same distance as the car in front of you, and use 25% less tires than they do.
If your fronts wear quicker, move brake balance rearward, if your rears wear first, move brake balance forward. LSD, most tracks favor a specific direction of turning. GVS has far more right hand turns than left, and your Left Rear tire suffers because of that. Turn your LSD Acceleration Sensativity down. All the way to 5 if that's what it takes to even out the tire wear across the back. Increase your downforce. Despite what some may think, more downforce DEcreases tire wear.