I hear the stock front sprocket is an absolute must! You will get a very annoying whine from an aftermarket front sprocket as the stock sprocket is the only one I have found that comes with the sound dampening rubber.
I can tell you not to by an RK X ring. I replaced mine about 16000 km ago, with an RK as the much loved DID was not available at the time at my local shop.
Now I have a Pro Oiler on my Bandit, and I know that this chain was well lubricated every second of its life, but it has developed a tight spot in one area. (Close inspection of the X rings and links show almost new condition). While the chain is running on the bike, imagine holding an elastic band between two fingers & stretching it slightly, this is what the chain looks like running on the bike. This happened suddenly and abruptly. (I believe this is refered to as elongation)
I am very anal at keeping my chain serviced (I regularily check tension, and with the Pro Oiler, the chains is very clean & well lubed at all times.
I have never in my life seen a motorcycle chain do this ever. I will never again buy an RK chain.
I will be shoping for a DID shortly.
Not only is the DID rated the strongest, it is also has the lowest friction rating of any chain (according to DID)
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You can read about it at their site.
http://www.didchain.com/xring1.htm