55 psi should work very well. I ran up to 75 psi in my 185/70R14 on the Escort lol. Once you get around 50, you start dealing with the Law of Diminishing Returns unfortunately
Darin (MetroMPG) has an excellent writeup on inflation pressure ->
Coasting distance vs. PSI!
Edit - I run incredibly high pressures to wring out every last 0.01 mpg that I can get! Just so you understand the insanity