How many cars are you testing with Marty?
I only really tested for wear and there are only gt2 or gt3 tyres in all the gt cars we are using. With just the 458 m3 and p4/5 running the gt2 tyres all others use gt3 rubber.
For wear teats you only really need to try one of each and having done laps in each of them at some point have found tyre life at 100% to be quite similar depending on tyre type. Setup will have an effect and some cars are a little better on tyres then others but the differences are quite small. At the 4x rate you dont even notice such subtle things as the tyres just all die fairly quick.
Fuel wise is what really needs testing in all cars and Wally has done this. Just a pure guess id think the evora's should be best on fuel but they are well down on power. I did hear guys say rhe merc sls was not using much fuel but also the 1.06 patch did alter fuel in some cars so things may have changed a bit.
The few cars I tried were getting 12 to 14 laps at Silverstone at 3x fuel and 45 min race with a pitstop would be around 21 laps there.