When I upgraded from 135 bhp to 227 bhp, I found that 185s were a little lacking in the traction department (wheelspin in 3rd if being brutal ) so moved to 205s. This improved traction but also introduced some unwelcome understeer which it took a bit of set-up tweaking to eliminate. So, if you bear that in mind, a move up in tyre size is probably a good idea at that power level.
Yellow SL #32 - member of Drowned Rat Racing