You shouldn't have to regear that thing at all.
I run around little over 55pmh all day long on my stock gearing, variator, and pulley. It's variated for a reason!
But if you want to keep up you might think about getting a performance variator like the Varplus from Malossi. It'll give you better low end and higher top end.
Otherwise, just do what Davey is telling you to do. There's lots of potential in the Airsal kit. It should do 50 pretty easily.