Actually, diablo III plays very well on an MBA. I have a gaming desktop and also the MBA (core i5). Settings are dialled down, but honestly can't tell that much of a difference vs. the two. It works every well on the MBA. Yes, FPS is low, but it doesn't seem to matter for this type of game. At least it doesn't bother me (and in other games, the FPS being low really bugs me).
I disagree with this because I'm getting the feeling you're still on normal difficulty. At the very minimum, you want 30 fps consistent regardless of what's happening if you want to survive hell and higher. If you have a low vit character, even nightmare can be annoying if your frames drop below 20. You can forget about hardcore too.
That being said, the 2011 (and even 2010) MBA should be able to handle the game through boot camp in the worst case scenarios.