From personal experience I can say the stock carb both works and performs better than the cns... I got one about a year ago and got it tuned (which is no easy task) took it for a test ride and it wouldn't behave its self so back for more tuning... finally got it to behave but it didn't perform as good as the stock nt carb did. I put the nt back on and got my bike up to 42mph consistantly, and did it with the 44 tooth rear sprocket. I also weigh about 225...
If you want a good combo for speed you'll need to do some port work or get a ported cylinder, then you'll need a good exhaust... most the pipes on ebay are junk or wont perform... the outlet on most these pipes is way too small and restrictive to get a bike past 30mph... you can easily gain a few mph as well as better acceleration just by removing the end cap off the stock pipe and drilling 4 more holes 5/16" thru the end cap then put it back on... if you got the stock pipe and do just this trick you will feel the difference and see 3 to 5 more mph...
A good performance pipe like the sbp pipe will give you a very noticeable improvement once installed...
Like mentioned above tho... your bike wont have a good top speed until the engine has gone thru a few tanks of fuel, its best to run a new engine on the rich side to help keep things cool and tune after the second tank is finished. You'll feel it when your engine begins to break in and the rings get seated.