Unless you are racing or heavy into trackdays don't bother. I have a 520 on my GSXR and do like 15+ trackdays per year and race my R6. You won't feel a difference from a 525 to a 520. Going from a 525 to a 520 is still saving some weight and is less rotating mass for the engine. On my R6 the stock chain was a 532 (which is bigger than a Busas chain) and when I went to a 520 you could tell. If your current chain is older and you are replacing you could get a 520. Just be sure to change your sprockets at the same time and get a quality chain. If you want to feel a difference you could go -1 in front or +3 in the rear or do the common -1, +2 combo. On my GSXR I did +3 in the rear because if you go down in the front, the engine has to work harder.