I want to get some new tyres on the SE and I want something that will grip grip and grip.... did I mention grip?

The tyres that are on there currently are rubbish, cheap and nasty's that were fitted by the dealer to pass RWC before I bought it and needless to say perform similarly.
I'm thinking a set of the Dunlop Direzza Sport Z1 Star Spec, which are apparently very good. I'm not sure I want to get R-comp tyres as the car will see some light street duty, that said, it will probably get dríven 3-4 times a month as I want to start doing some club days.
My question, stock tyre size is 205/40 R17, what would be the result of going to a 215/40ZR17? I wouldn't mind a slight increase in contact patch all round as my supplier doesn't have it in a 205?
Is it ok to go ahead and get these in 215/40?
If it is a big issue, they do have the Bridgestone Potenza RE-01R in 205/40.
Thanks,
Dino.