For $700, you do not want a 4GB graphics card in a laptop. The only 4gb laptop models in that price range have terrible performance. They throw cheap, slow memory onto a low powered card and take advantage of people who don't realize that the amount of RAM is not very important for GPU performance. You want to find a laptop with a good GPU. You can safely ignore how much RAM it comes with because any good GPU will include the proper amount of RAM it needs to perform optimally.
For $800, the Dell Inspiron i7559-763BLK is a great buy. The GTX 960m is a pretty good card for a laptop.
If you do go for a laptop with the 940m or 950m, make sure they use GDDR5 memory and not DDR3. The slower memory can have as low as half of the performance...