I don't see a 500 in this bike's future. The more I read about it from folk who have done it, it is not in fact a bolt-in. So far I see rear upper engine mounts need to be redone, the sprocket needs to be shimmed, fitting the coolant lines/cap requires mod; all to get an unbalanced point-and-shoot machine. It seems to miss the point of the original bike.
I like this bike with its original 250. The 300 is better because of the head and intake design, not to mention the cc bump. I could see that motor in this frame still being "fun"; the 500... not so much. But that's me.
Also, I have an sv650
Sorry, those beat out the Ninja 250/500/650 family on all counts! But that's just me...