The Tak is a faster scope than the C11....greater FoV, therefore smaller image scale for things like planets, pn's etc.
As far as firewire vs USB goes, firewire is nearly twice as fast but you may not have a firewire connection on your computer. I'm lucky with my Mac, as they come with firewire sockets. Some of the dearer pc's will have firewire, but you may have to get a card and plug it into your pc.
Your assumptions about scope/imager performance have been pretty much spot on there. Here's an article from
Sky and Telescope that may help you with a decision. Id be inclined to go with the ICX424....it's not overly fast, although as we mentioned before, you probably won't use the full 60fps for most situations. The KAI0340 is insane....200fps would be unusable on anything under 0.5 metres as you just couldn't gather enough light to keep up with the chip. You'd have to dial it down considerably on a smaller scope. Mind you, your images would be guaranteed to be rock steady even under poor seeing conditions. But what would be the point in stacking 44 million images gathered by a 180 or 250mm scope just to be able to see the pic!!!. That's why you need the lightbucket. The 648 x 488 pic size will give you a good image with the ICX424. Look at Mikes pics....his DMK21 is only a 640 x 480 camera and he gets great piccies. However, although his camera does 60fps, he probably only images at 25-40fps on good nights with bright targets. Dimmer targets would necessitate slower frame rates in order to image the target.