Hello Jerry,
Supposedly, the reels for the 2500 series film tanks, being quite a bit larger than the 1500 reels, allows for a more even flow of chemistry to the film surfaces. I own and use both 1500 tanks/reels and 2500 tanks/reels and have never noticed any discernible difference in the negs. Nowadays, I do tend to use the 1500 tank for 35mm and the 2500 for roll film mostly because the former requires less chemistry. In the past I've processed many rolls (120) of film in the 1500 tank and always have gotten beautiful, even development. I guess, in theory, the larger 2500 reels would be better for the processing of roll film using a pyro-type of developer whereby aerial oxidation is a concern. I wouldn't worry about it too much, though. It will probably come down to what's available for purchase...
Good luck!