If you already have a 500c system with lenses, I'd say stick with it. Unless you find yourself saying "damn, I really wish this body had (insert option here)" or "I wish my lenses produced pictures that look like the T* coated ones" on a regular basis, what you have is fine. I have the 500cm with 3 lenses (up for sale actually in the classifieds) and they're all T* and I'm more than happy with them. I wouldn't upgrade for twice the price to a 503 with 3 CF lenses because it likely would no equate to better photographs at the end of the day, which is the point, right?