Jamie_Williams3 said:its more about the clamping force of the caliper than the size of the disc, if you wanted "ultimate" braking force then you would be talking 6pots and by the time the disc was affecting the braking rather than the other components, you have one very serius and expensive set-up.
the downside to the 285 vs 260 is, the extra 25mm of disc doesnt really make the braking much better and taking into consideration the extra £££ and handaling issues of having a bigger disc alot of ppl decide against it.