Dont waste the money on a 525, it is not needed on your bike. I will say if you buy those "ebay" kits you get what you pay for, skimp on a chain and sprocket and you should expect to only get 5000 miles out of them.
I wouldnt use a vortex sprocket to throw at a fence much less on my bike. Had one, it dies in 1000 miles. had my test it at his work (GM) and it was not even hardened. Called vortex adn they would not stand behind it even though it was a manufacturing defect as they advertise they are hardened.
I personally would go with a DID either the VM series or the ERV series. They are a bit more, but they are also the better chains that DID offers and have over a 8000 tenstile strength rating.
I would also use a Renthal rear alum sprocket, They offer a hard anodized series. Once again pricey but you get what you pay for. I had over 10,000 miles on my 03 636's DID/Renthal setup and I am far from easy on my my bikes. I ride them like they are to rode.
And just for the person that is going to say you ahve to change both of the sprockets, I never once changed my front on my 636. I had over 26,000 miles on the factory front and it was in perfect shape when I sold the bike with no wear what so ever on the sprocket. I also clean my chains once a month and get all of the lube off of it and also clean the sprockets as well.
if you want a better rear sprocket, there used to be one called a Stealth sprocket. Alum carrier with a steel tooth section. Last I heard Sprocket Speacialist bought them out. They are really pricey, over the $100 range for them but they last and look nice.