well I went with the 520 which is -1/+2 (down one in the front and up two in the rear) and I love it. Its a completely different bike bro. i think you only lose something like 7 mph in sixth gear? Its quick off the line and can come up in first and second fairly easy. beware though any change to your sprockets like a 520 c0nversion kit will throw off your speedometer and your odometer and therefore your bike will say your going faster and traveling slightly MORE miles. its not a big deal if your planning on keeping your bike.... but if it bugs you you cal buy a SPEEDO HEALER for like 120 i believe on Ebay. Good luck! let me know what you decide!