im new here just wondering how big a change is it when you change the numbers of teeth on your sprockets from stock to anything different

 

Its pretty noticable -1/+2 is probly the most common. gives ya some more torque when you're taking off, makes it easier to wheelie, but the top end will suffer some, i.e. when you're on the freeway it'll be running at higher RPMs. Dont know what you're riding, but stay away from the 520 kit. Stick with the 525 (or 530 for litre bikes). Those numbers dictate the width of the chain, and the wider the chain the stronger it is. And the difference between weight (same kits diff. widths) is only gonna be a few ounces, the biggest weight reduction comes from the aluminum sprocket.