What should my next upgrade be?

So I've been thinking this over for about a month with no conclusion. I'm still unsure whether I should upgrade my video card to a XFX 4870 1GB or other accesories: Dark Knight cpu cooler, extra 1 GB of RAM? Please help me decide!I want the cpu cooler to overclock my cpu further but I really want a new video card!my spec:Sigma Gaming Unicorn Mid-Tower
Asus P5Q Pro Intel P45 CrossFire Chipset
Intel® Core™ 2 Quad Q6600 @ 3.0GHz2GB RAM 800Mhz
Stock Intel CPU Cooling Fan
HIS IceQ Turbo 3 ATI Radeon HD 3870
Thermaltake 600W power supply

I would say upgrading the ram is top priority and get instead of 1GB of extra RAM, 4GB of ram, like some nice DDR2-1066 Corsair Dominators and get rid of the 2GB you have now, that should improve overall performance of the system. Or get more identical sticks like those and place them in next to the ones you have now, but getting 2x2GB would be better stability wise especially when overclocking. Then comes the graphics card and since the Q6600 will not bottleneck it at 3Ghz, a CPU cooler comes in third place in my oppinion.

1st:Â Ram
2nd: Graphics card
3rd:Â CPU cooler