This discussion is always interesting to me given all the variables that go into "how much" is enough.
I have been driving my dad's 1993 RX-7 FD the past week: Holy acceleration and handling, Batman.
The thing weights 2130lbs and has only 252HP matriculating it down the highway, but it could be considered irresponsible since taking 45mph corners at twice that in soundless, soulless competence without much driver skill isn't in the Highway Patrols definition of responsible.
I have driven that same corner in a friends late '90's convertible Mustang 5.0 that weighed nearly a thousand pounds more with 25 less hp than the RX-7 and I felt like I was going to depart the roadway at much slower speeds: The suspension and tire set-up helped the car alternate from wallowing to skittish insouciance in the same corner.
Anyway. HP isn't the measure I use. Our family car was a 1968 Ford Country Squire with the 494 cubic inch motor that had itty bitty drum breaks all around riding on 8.45/15 tires with a curb weight over 4,100lbs: That was irresponsible
