You would need to mount the wing further forward if you went with any sort of a "jet fighter" amount of sweep.
I'll bet the most noticeable improvement comes from a thinner airfoil and finding the prop that marries the engine to the new wing.
A good plane to look at for design ideas is The Rifle by Angel RC. Angel uses simple construction to create a design that looks more complex / exotic than it actually is.
If you stick with the basic Q500 layout, [except make it thinner everywhere you can] they are hard to beat in general.