Jackson, of course... they are famous for that.

It depends on the Ibanez. Some of them have a really sleek neck that plays like a Jackson, and some have a big honkin' neck that plays like a Gibson or Fender. "Faster" is an objective question, some people don't play faster on a thin neck.
But between the two, I'd get a Jackson. For most models, you're probably getting a better axe for your cash.

I use Ibanez for my recordings. I have S series- S2540. That's one of the best guitars I have ever played. I would say, that Jackson dk2 is much worse than S2540 (but dk2 is much cheaper!).
You shuld always keep in mind what are you using guitar for!

indeed, he asked for the sleeker and faster neck ;)
btw, the cost is too much different.