If you don't want the chip to throttle, the simple answer is to get the Macbook Pro, not hack together a crappy laptop from a Mac Mini :)
Even then, the throttling on the Air seems pretty minor. About ~30% drop in performance after it levels off, which takes several minutes. Less if you get one of those pads with a fan in it that blows on the case.
Even then, the throttling on the Air seems pretty minor. About ~30% drop in performance after it levels off, which takes several minutes. Less if you get one of those pads with a fan in it that blows on the case.