I ran Hoosier DR's 275/60R15 on my car at 16-18psi the more tire pressure the faster you will be, but if it spins try dropping 1/2 or 1 lb air pressure.
I found it best for me a 18psi. Like they said, more is faster but you also need to find out what works best with your setup. That's where a good test and tune track day is great because you can start high and keep lowering to find the best.