Well-

You want as much speed as possible? If you are serious about that, try a Nelson, MVVS GRRT, or a ducted fan engine like the OS-46VX or a K&B 7.5...120-130? Yeah and then some

If you want a powerhouse that runs out of the box and that you can use on many airframes in the future- The Jett is the obvious choice. The Rossi-45 is a beast but kinda heavy for a Q-500, a Webra-50 is also a great sport engine to stick on there...

Is there a price range, fuel preference, or future airframe we should consider?

I have both the Jett-50 and Rossi-45, and I USED to have an Irvine-53 (great engine!) but those 2 are a step above the Irvine when it comes to revvin!

Keep us posted!
james