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)
You can read about it at their site.
http://www.didchain.com/xring1.htm