What the hell are you doing running your tyres at 40PSI?
They're only rated at 33 to 36. If you run them over inflated like that, and might I say grossly over inflated, you are gunna get poor tyre life. The tyre guys aren't going to care though, they'll go along with whatever theory has been sent your way about better traction and performance cos you'll have to buy more sets of tyres than the next guy.
Seriously running your tyres at 40PSI is awful bad it will cause extra wear on not only your tyres but your spine!!!, shocks and bushes. The COPS run their pursuit cars at 35PSI and they test thier cars every night chasing WRX's (I know they never chatch them

). With the type of tyres we run a 2-3PSI makes a huge difference in the way the tyres hold the ground or don't... Just remember if your tyres are too hard you'll risk skipping and you are really giving yourself less tyre to the road with an over inflated PSI, and less rubber is never good.
If your run your tyres around 35 you have the best of both worlds... Better wear and pretty good grip.
Good luck with it.