I'm not sure if your intentionally only considering the 510 and 520 or not. If not, I love my 580's. They're bigger, but they match the size of the headlights nicely. Plus they're very bright. Of course, they're probably more expensive. And I don't like the grids in the other models either.
If you go this route, get the driving lights. They're not to wide an angle and not too narrow. Aim them a little higher than your low beams. They're bright enough that if they're on, then you flip on your high beams you barely notice the high beams coming on.
I mounted mine on a Warn light bar. I'm not sure that they'll mount on the existing holes, but I think they'll fit. I included both front and side views of mine so you can see how they relate to the size of a double brushguard. They're rounded enough on the back that I bet they'll tuck between the lower and upper bars on the guard. The only issue I imagine would be bolt length, whether they'll reach through the brushguard bar (I don't know if you have holes in your bar or a clamp/tab). If that's a problem you could probably make some mounting tabs that would work.
