I don't know Craig Wilcox or his car, but I understand that he is a solid driver with a well developed car. The Mini beating the rest of the STX class is partially due to course design. Day 1 times were close, with several cars within a second of Craig, and on the 2nd day, he beat everybody by over a second. I read that there were places on course that Craig didn't touch brakes where everyone else did. I understand that the Mini was on 225 tires. I'm guessing that the Mini's short wheelbase doesn't make it a paragon of stability, and with 225s the Mini isn't winning on outright grip. I've got to believe that light weight and narrow width were the 2 biggest advantages the Mini had over other cars in the class. The FiST has both of those, but slightly narrower and slightly lighter. The Mini does have a very well designed suspension over the FiST.
I have run mis-matched tires on the FiST, but not with the goal of changing overall balance, but because I was trying to limit my risk when finding out how much tire you could run on the FiST. When I first bought the car, I ran with Dunlop Z2 and BFG Rivals. Like I said before, the Rival was too much tire, but I still drove them till they were used up. I switched between the Rival or Dunlop up front based on the course walk, using the Rival to get the most speed out of 2nd gear, and using the Z2 on slower/ tighter courses. I wasn't able to tell meaningful difference in balance when I switched.
It hasn't been my experience that the FiST has trouble rotating though. In slow corners it helps to toss the car a bit for rotation, but unavoidable understeer is not a problem for me. In my mind, the most difficult part about driving the car fast is wheelspin. At slow speeds and very tight turns, the inside wheel lights up every time. The e-diff is a piss poor substitution of a differential. This causes 2 problems- the first is that the e-diff works the hell out of the brakes. I've come in after 2nd runs and sprayed the tires; the brakes were so hot, and transferring the heat to the wheels that water on the wheels was sizzling off. The second problem is that we can't get enough camber (in Street class) and so the car really overworks the outside edges of the tire. When the car spins the inside wheel, the tires are just too easy to overheat. I've come back from events with the edge of the tire turned purple from the heat.
To address the e-diff, I'll be installing a true LSD. Well, a torque biasing differential anyway. I'm also going with a set of offset LCA bushings to improve the camber curve when turning. I think that the lsd is going to be a huge improvement. I'm hoping that improved bushings help to minimize the bad things that happen to macpherson suspensions in corners, and get more out of the tires.