I had a Maxxis IT last year, excellent tire especially in the wear performance. I am not good enough to tell tires apart from a traction aspect so to me they are generally about the same. KX500's just blow the rear tire off anyway, so I will more focus on "longevity". I've run Maxxis for years now. AWESOME tire and an awesome tire for cheap money. Dunlaps are overrated IMO. Yes they are a great tire, but they are a great tire for a month, then they are junk.
Right now I am running a Dunlap 739G it's a 120/80-19. I specifically wanted to see how an 80 series profile tire would behave cornering wise on my 500, and I must say I like it a little better. You get a little less traction, which is actually a good thing when cornering a KX500. On the downside, I don't like the 739G in the woods, as it bounces hard off obsticles from less sidewall flex vs. a 90 series tire. And just like all my other Dunlap's the longevity is ok, (but nuthin' great for a $90 tire). So probably going back to Maxxis next time around, maybe Maxxis might produce a 120/80-19 in the IT........ (Hey Maxxis, you listening ?) LOL