Travymoto, whats been going on, XB8 huh? Sweet.
I run the Mugen pistons mostly because i'm more fond of a machined teflon piston then a molded plastic one. I think the stock ones may deform under loading also, but that's only a theory.
I use 5-7-3 in my diffs and 1.4mm mugen pistons with 35 ft and 35 rear. I also have found the car to very sensitive to ride hieght. I run my car pretty high except on very high bite tracks to avoid rolling.
I also like the zero roll center bushings in front. For tracks that feel too hooked up, move the rear hubs back, or run less toe in back as you've done........should be a rocket,
.......ttyl, Jim