Asking too much of my P650SE?

Hi everyone,

I have a P650SE with 8GB RAM and 970m, 3k Display.

I'm trying to use it with a cheap korean display, the manufacturer states that they are not compatible with laptops and require a desktop Graphics Card. To hook it up with my laptop I had to use a Dual-Link Display port to DVI adapter. (http://www.apple.com/ca/shop/product/MB571LL/A/mini-displayport-to-dual-link-dvi-adapter).

I'm having issues gaming and alt-tabbing while using the external display(game crashes,...

Asking too much of my P650SE?