I had a lot of control issues above 35 when I got the 58, but after going through it and replacing the wheel bearings, king pins, and tie rods, it is rock solid up to 85 (I have not tried going faster).
I am running the stock(ish) 283 with a T5, a 3.73 rear end. I can't comment on the higher power question, but I have no concerns with the suspension design/capabilities as long as it is in good condition.
I will say that if you are going to put in a high power powertrain and go fast, upgraded brakes should be high on your list as well.
