The 500R looks like a sweet case. 600T is a little different up top, but I think the 500R would handle a rad up there with a set of fans if you wanted one. The hard drive cage does not look like it's removable, or separable into two cages like the 600T can.
However there are two fan mounts on the 500R hard drive cage, and it looks like another fan mount on the bottom of the case which is a big plus I think. It also uses 2 front 120mm fans in place of the 200mm, which some people prefer (I don't mind either myself).
Most of the rest is aesthetics. They both look pretty nice, but I have to say I like the curved convex 600T side panels over the angular type the 500R has, but that's just me.
The features you get on the 500R are excellent for the price.