I would be surprised if going to a 40 profile would make much difference as I have seen a few sags running 265's on the rear and the guys running 19,s also have 265's.
It's just I've managed to find some eagle f1 v tread gsd3 or whatever they're named original equipment tyres in the 40 profile as I'd rather use them than have different fronts and rears, no 35 profiles anywhere!