I have tried a bunch of combos but the best in my opinion is 2.7 both front and rear. I have gone up in the front oil to 400CST and 350CST in the rear. I think the balance is a bit better with the thicker oil up front. I will also say that the 350CST from Xray seems to be thinner than Muchmore 350CST. Either way the car feels better with the Muchmore oil all the way around. The Laziness you feel initially is probably more of a camber issues then anything else. The T4 seems to be able to handle the transitions of weight from side to side a bit better than previous platforms. You have to drive the T4 hard to get the lap times out of it, but luckily the car can handle abrupt direction changes very well. Also a couple of other options would be less ackermann shims or some toe out to help with initial turn in.
A couple of things about the T4 from my testing...the car rolls a lot and as such light weight bodies make a huge handling difference on this car more then the T3. The car is the best with Lightweight bodies. The car stays flatter and tends to have better corner speed.
The shocks need to be maintained...I have personally noticed that the o-ring on the bottom tends to allow more oil leakage then previous versions. This makes for a smoother shock but also more maintenance. I will say that the shocks are very nice and I am pleased that Xray finally included aluminum shocks with the kit.
I think overall the springs designed for this car tend to be too soft. Even the 2.9 springs feel too soft to me, especially for the slower classes. You end up scrubbing off speed with the softer springs, at least with my setups
. I am pretty sure that Xray was concerned that the shorter springs would feel stiffer on the car, but in practice they seem a tad too soft.
With the additional amount of chassis roll it tends to gunk up the motor side of the chassis very easily. Make sure you keep the bottom of the chassis clean.
As weird as it sounds I am working on trying to make the car roll less to keep if more efficient through the entire corner.
Like most Xrays I have driven the car seems to suffer the most mid to exit, but I will tell you that the T4 has improved this over the T3 platform. Now it seems the car rolls to deep into the middle and kind of gets stuck. With some more setup work I think this can be fixed, but not quite there yet.
Setup wise this car is different then the T3...and it reacts to changes better then the T3 so far.