can donut me your 6950 when you're upgraded?
need to squeeze out every last bit of juice over here too

depends on games really, CPU heavy games like BF4 or SC2 might not have that big an impact, though most games now are GPU heavy as seen in PS4/Xbone design.

IMO, just do it, though personally i'm now stuck with 2nd Gen i5 and CSGO, im contemplating whether i want if harga kasih sayang is not harga johnny waka black label or below.

i think cukup2 makan or maybe bottleneck a bit.. currently did you experience any game using your cpu like 85-100% all the time during gaming? try with bf4 and also dota2 and check your cpu usage with the current gpu..
if yes, then most probably 280x also will be bottleneck by the cpu..