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will you be doing a lot of gaming? macworld tested all three and found, w.r.t. to the graphics:

In Quake, the high-end model was more than twice as fast as the low-end model and outpaced the mid-model 2.66GHz by more than 10 percent. We observed similar disparities with the Call of Duty 4 test: again the high-end model squeezed more than twice as many frames per second as the low-end model but was on par with the mid-model. If you’re a gamer, you’ll benefit from the dual graphics setup. Plus, the high-end 15-incher has twice the video RAM of the mid-model.

you can see the benchmarks here:
http://www.macworld.com/article/141185/2009/06/15inch_macbook_pro.html
 
nice one. The article is a bit outdated, i.e. they didn't run Snow Leopard in testing. But I'm guessing The middle version is 10% slower the third and the tird is twice as fast at the first. I am only saying based on the quote you said. I'm in no way a pro in this kind of things. I probably gonna wait 2-3 month before apple integrates Snow Leopard on new macs, and fix stuff on it, to save me some problems + 10.6 update will come out to fix some stuff on the Snowy.
 
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