So both of them should work within your computer.  It's basically just the VRAM amount that is different. If you're getting this for gaming modern games are definitely starting to utilize lots more VRAM but the age of the card and it's overall performance you probably won't see much of a difference considering it's usually the higher video settings that cause the VRAM usage to soar. If you can get the 6GB one for just a bit more money it would be worth doing but if it's a large increase it's probably not worth it as you likely won't be running the settings that would require the higher VRAM amount anyway and it's only beneficial when you literally run out of it and need more on your card.
Hello, I have a few questions I'd like to ask. I own an Alienware X51 R1. I was considering upgrading the graphics card to a GTX 1060. I can't seem to understand the difference between a GTX 1060 6GB and a 3GB version? If I get the 6GB version will it not run with the computer, but the 3GB version will? What's the difference between the two? Would it be better to get a different card? I'll take any help I can get!
X51 R1, GTX 1060 6GB vs 3GB?