I never heard about getting better colors on 1080p monitor using display port rather than dvi. As for g-sync that depends on your framerates. If your games run on your rig at stable 144 fps, then g-sync is useless. You will only notice difference if your fps vary a lot. I probably wouldn't bother with it at all unless my fps drops below 60, but in that case it's better to invest in more powerful GPU rather than g-sync monitor.