You need the second stick of 4GB RAM to get the video speed up.
Borderlands 2 is very playable at pretty high settings. There is a small lag as a new scene loads or pulling up the inventory but it does game very well for the dollar.
It's just missing a stick of RAM.
Its the Asus K55N-DB81
Here's the specs:
1.9GHz AMD A8-4500M Quad-Core
4GB of 1600MHz DDR3 RAM
500GB 5400rpm Hard Drive
Integrated AMD Radeon HD 7640G Graphics
15.6" Widescreen LED-Backlit Display
1366 x 768 Native Resolution
SuperMulti DVD Burner
802.11b/g/n Wi-Fi, Bluetooth 4.0
Integrated Webcam, Microphone & Speakers
Windows 8 (64-bit)