Deciding between these laptops

I'm going off to college next year, and am deciding which laptop to buy. I have it down to two different laptops right now, but can't decide which is better. I'll be using the computer primarily for gaming as well as standard student work. Here are the specs:

Lenovo IdeaPad Y560(0646-2EU)
- Intel Core i7 720QM(1.6GHz)
- 4GB DDR3
- 15.6" screen
- ATI Radeon HD 5730 graphics
- 500GB Hard Drive

Asus G72GX-RBBX09
- Intel Core 2 Quad Q9000(2.0GHz)
- 6GB DDR2
- 17.3" screen
- NVIDIA GeForce GTX 260M
- 640GB Hard Drive

The thing I'm most worried about on the second laptop is the DDR2 memory, so how much of a difference will that make?

Edit: also thinking of this one, which was recommended by a friend

Asus G60JX-RBBX05
- Intel i5 single core(2.26GHz)
- 4GB DDR3
- 16" screen
- NVIDIA GeForce GTS 360M
-500GB Hard Drive

I'm not sure if the loss of multicore is worth the improved graphics, though.

It's not so much the DDR2 that will slow you down as the processor, which will be slower than the i7 despite the frequencies. A single-core i5 is not really going to work out as much.

The 15.6 screen is what res? a smaller res might be an advantage, if you want eye-candy and fps. The stronger processor might be an advantage in more CPU intense games (strategy).

The difference would be how hard the video chip is stressed while gaming. You want to run games at native resolution, so the smaller res could have higher settings in games and so would look better... but a 15" screen might be too small for you to game on easily. I myself would need more, but then I have a desktop for gaming.