The AMD desktop is CPU limited vs. the laptop which will outrun it in bechmarks.
The desktops video card makes it a better gaming system, but combining the same video card with an intel CPU would give you a much better gaming rig. The AMD FX-8120 is just not that good a gaming CPU. http://www.tomshardware.com/reviews/gaming-cpu-review-overclock,3106-5.html
FX-8120 games comparable/lower gaming performance than Core i3-2100T, i3-2120T