Get the i7 720, as it's a true quad-core capable of 8 threads at once, whereas the 620 is a dual-core that can handle 4 threads at a time. In terms of video editing and rendering, the CPU matters much more than the video card, as most editing software uses exclusively the CPU for these tasks. The ones that support video card acceleration often just support the high-end nVidia and ATI workstation cards. A lot of RAM, a big hard drive, and a high-res screen are also important for video work. Forget about those $4000+ gaming laptops; instead, look at this page on newegg with all their i7 laptops:
http://www.newegg.com/Product/ProductList.aspx?Submit=Property&Subcategory=32&Description=&Type=&N=2034940032&srchInDesc=&MinPrice=&MaxPrice=&PropertyCodeValue=393:49576
Then there's this ASUS model with an i7 720, 4GB RAM, 500GB hard drive, a full 1080p screen, and a GeForce 360:
http://www.newegg.com/Product/Product.aspx?Item=N82E16834220700
It looks really, really good for $1200.