Where did you hear that about dirtying up? I've never heard nor experienced that.

I have a 257 AI that I love. LOVE. As others have said, there are no downsides to AI'n in my mind. You won't likely get a ton of extra FPS, but case stretching is virtually non-existant.

As a matter of fact, I'm building one for a buddy of mine right now. I'd go for it... HIGH cool factor...