I have a 530 chain/sprockets.
I don't race it and the weight (4 Lbs of chain) doesn't bother me.
My thought on that was the 530 is a wider chain and the load is spread over a slightly larger area than a 525 or 520.
That way, it might allow more life out of the aluminum rear sprocket.
And I went with a hard anodized rear sprocket for even more durability.
You can use a 520 or 525 chain/sprockets.
The 525 chains are very good these days and are now standard equipment on the '09 GSXR1000's, or so I've heard (but not verified).