Personally, I would stay away from an Aluminum rear sprocket. They wear out fast. Stick with steel and it will last a LOT longer... and for the 520 conversion... unless you are hitting a LOT of track days, and riding at the expert/advanced level, you will NEVER notice the performance difference...
Gear it down some yes, thats a big difference. Drop a tooth on the front.
If you stay with a 525 chain, I have a rear sprocket (steel) posted in the for sale section. Brand new $30 picked up $40 shipped.
on my 97 ZX-7R I went down one front and up 2 or 3 in rear (cant remember). It killed my top end, and the rear Renthal was Shot in one summer. It was something like a 48 tooth, and had about 17 teeth left. Which also kills the chain... It was a true waste of money.
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