Tuz - your sidewalls should be stiff enough to happily run around 30psi if you crave a cushier ride, but I'd keep 'em at 34-36psi to keep the tyre wear even. Tyres also clear more water with higher pressure, as well as giving better fuel economy and giving more grip, as they distort less and keep a more consistant contact patch.
I have seen LOTS of tyres that've been run @ 26-28 psi around ~10km of corners, and the outer tread shoulder is completely gone, and some of the sidewall has been scrubbed off - yet the centre-inside of the tyre is pristine. - So I'm not messin' when I say not to run ANY passenger car tyres @28psi ! ! !
-I run all my car tyres at 38psi b.t.w. - primarily to get good feel for the contact patch through the steering and . . . MY ARSE !