Upgrade on new build?

[Veesofnaught]

I am debating whether it would be worth it to upgrade a few components in my system or simply wait and do an entirely new build. My specs are as follows:

ATX Mid Tower
585W Power Supply (2)+12V Rails
ASUS P5QL Pro
Intel Q6600
Arctic Cooling 95 mm CPU Cooler
G Skill 4 GB DDR2 Ram @ 1066 MHz
9800 GTX+ OC
160 GB 7200RPM HDD for OS
1 TB 5400 RPM HDD for Data
24" 1920 x 1080 Monitor

My primary use for this system is for gaming and video editing. I have roughly $500 - 600 for upgrades, but I will have more later if I wait to do a whole new system. Currently, the games I am playing run okay at 1080P but I have to turn some visuals down. I am leaning towards a new video card (ATI 5870 so I wouldn't have to upgrade for awhile) or a new processor (i5 750) but that would mean a new mobo and RAM. Obviously the video card would give me more performance in games, but would my current processor and RAM bottleneck a 5870?

 

[Veesofnaught]

EDIT: Because Tom's is not letting me edit the original message, the title should say Upgrade OR new build. My system is over a year old and is not a new build.

...just thought I'd clarify.