I'm not as big a guy as you, and I put the psi of mine up to 60 or 65. When I started regularly commuting earlier this year, I was 200 lbs. Right now, I'm 185. I haven't lowered my psi at all, since I like the way the bike rolls with the higher psi. I do have a few 700C bikes, and when I ride them, I put the psi at 110~120.

Whether or not you should add more air to yours depends on:
A. do the tires look low when inflated to 55psi?
B. do you ride on relatively smooth surfaces?
C. Most importantly, can the wheels handle it? (will the tire beads pop off the rims, will the tubes find some little nook or cranny to escape out of and burst -- don't scoff... all of these things have happened to me at one time or another over the years that I've been cycling)