Hello, I'm new here and new to cycling. I have a wal-mart special right now but intend on upgrading this spring. I ride on rail to trail, some city riding and I live in the country on a gravel road, which I ride on quite a bit. I ride around 50 miles per week. In layman's terms, what is the difference in the trek 7300 at $469.00; the trek 7500 at $659.00 And The Trek 7700 at 1259.00? Just wondering if the higher priced bikes are really worth it. thanks...Lewis b.