high memory or high RPM?

I am currently creating my new laptop, first one, and i want to get the best. there are two hard drives i am debating between, one is [640GB 7200RPM Hard Drive] and the other is [1TB 5200RPM Hard Drive] i want a lot of memory (as most as possible, but at the same time i dont want to sacrifice to much of the speed. I am going to be an architect student, so i will be using lots of cad and photos and presentations. if i have to eventually use a seperate external hard drive i could, but im avoiding that at all costs. so can someone please explain to me the differences. i know about the heat and noise, which i would not enjoy to much, but i could easily live with it. i just want a computer that will suit me better. thank you.

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