my idea (just from experience) is that somewhere between 300-325 hp at around 3000 lbs +/- a couple hundred is enough for street fun. I felt my old 944S2 at about 200hp was a little low on power. My old Evo at "close" to 300hp was fun and the cayman is fun. Have driven some cars at 400HP + and just feels like overkillon street.

My cooper S at 168HP however felt decent, and I feel that at 200hp in that particular car , it would hae been enough (FWD, small, short wheelbase)...