Tire/wheel size help needed
 

Ok, so currently running staggered, with KWv3 coilovers, boosted.
Front: 18x8.5 35 225/40/18
Rear: 18x9.5 40 255/35/18

I am looking at getting some new tires, was looking to add just a bit more meat to these, as well as to upgrade to hankook rs3, or bridgestone re11 tires. Hoping to get a bit more traction. What is the largest i can go that would work with these wheel sizes?

I am thinking just bump up a bit to:
Front: 18x8.5 35 235/40/18
Rear: 18x9.5 40 265/40/18

This would increase the width just a bit, as well as a bit more sidewall. Or would you recommend more? Maybe something just a bit bigger in the rear? One other option also is to purchase 2 new wheels for the front to eliminate staggered and go full 9.5inch all around squared, of course if i do that, i will probably have to stretch the front tires a bit more for fit im thinking.

Thoughts?