Noel, I meant all-round performance. Originally you said 'I think my main concern is being able to take off fairly quickly as well as go up steep hills.'
That indicates that you want more torque rather than speed, hence my recommendation of a shift kit.
Now you want more speed, so buy an expansion chamber and a smaller rear sprocket.
That will make a bigger difference than a carb change. Many people have a lot of tuning problems with after-market carbs.
Sure, the shift kit makes the bike faster, a good 10mph in my case on flat ground, but it has all the other benefits as gears. Your engine won't be constantly screaming as you ride down the road, the bike will be controllable at low speeds and it will pull up any hill if you set up the appropriate ratios.
If you want more power only, the best increase for money is an expansion chamber.
Have you searched and read the reviews on these products?
I suggest that you do that.