As far as changing to a clamp on style filter, you need to consider a few things, what kind of riding are you doing. Are you going to be crossing a lot of water, mud running, etc..... If so I would not recommend going to a clamp on filter or running one of the higher flowing airboxes that are more open, due to the fact that they will allow water into the carb, and therefore the engine much easier.
If you are riding in just dirt and grass then yes you could go to the clamp on filter, and you would see an increase in power.
I dont know which would be a better kit the noss or the pro flow design airbox.