GTX 965M vs GTX 960M vs GTX 870M. Difference?

Hey guys, hopefully I can get some help here.

Currently shopping for laptop for work/moderate gaming. Looking for something under an inch thick and weighing under 5 pounds.

I've found a few laptops that fit the bill all with i7, SSD. But the GPU varies between the 870m, 960m, 965m. I do CAD and 3D rendering at work and play mostly CS:GO. Is there any huge difference between these GPU's? Is the 965M overkill? Thoughts/recommendations?

Thanks!

GTX 965M vs GTX 960M vs GTX 870M. Difference?