Imac or Mac Pro - Which is best for FCP?

I am about to purchase a new Mac Computer for use primarily with FCP and Photoshop. I've been using my macbook pro for about 7 years. I edit with FCP 5.0.

Recently, I've been trying to import clips captured with a Canon 7D. The .mov files will not play on my macbook. I took some .mov clips to the Genius bar for a test. The clips played perfectly on the store's computers. So, my current macbook does not have enough power for the new HD video files.

If I want to get the "best" computer for editing HD video content, should I get iMac or Mac Pro? Aside from the obvious benefits (price, iMac comes with monitor, etc...) what does the Mac Pro do better? Does it render files faster?

Will a Mac Pro with 8-Core and Two 2.26GHz Quad-Core Intel Xeon "Nehalem" processors allow me to render files faster than a Quad Core iMac?

Thanks,
Josh