I've never ridden a Banshee with 916's so I can't offer a side by side comparison. But like Rod said, mine is pretty quik for having stock port timing. I can't really say that it isn't ported, since I cleaned up the intake and exhaust ports a little. But I think I was the quickest Banshee there w/stock port timing.
But, I don't have a lot of top end. Don't get me wrong, it pulls as long as I need and want it too. But compared to the Rocket Pipes on broke's quad, the PT mids shut off a lot earlier. There was such a difference between broke's quad and mine that I didn't even find the end of his power band. It would reving so high that I was afraid to keep going and wait until the power dropped off.
The point I am trying to make is that the PT mids may not give you any more top end, but you don't need a lot of top end to be quick.
I have heard good things about the 916's, for the price of PT mids you could keep your 916's and have your cylinders ported. Without a doubt, you will be faster with this set up, than with stock porting and PT mids.
Matt