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I can't speak to the dedicated graphics card, so this is kind of a My Threads post for that.
However, I will say that I have been editing video in Final Cut Pro for about a year and I wish I would have gotten something a little bit bigger. The speed suits my needs since I am working on projects as a hobby. I have a 22" external monitor, but if I'm ever off of it I am dissapointed I didn't go for a bigger screen. It would have been worth it to spend a little more for me, but if you are always going to have it on a nice big external monitor then you shouldn't have to worry about it (although I would ask...if that's the case why not go with an iMac? Way more for the money).
Well in that case I'd strongly recommend a 15" :)
I can't remember, but I think that would solve your graphics card dilemma as well. It's definitely worth the money when you consider that your computer will last about 4 years before you want to upgrade.