Final part: 4870 vs 5750 vs 5770

I know this questions been asked a million time and I read the comparison but I'm still stumped.

I'm finishing off my pc and I'm down to the video card I don't want to spend more than $200ish CDN and prefer xfx for their life time warranty. I'm not a huge gamer (still rockin' CS Source) but I do spend a lot of time on my computer.

I'm wondering if I'm good with the 5750 but I can get the 4870 for the same price. The 5770 is an extra $40 bucks so I'm really not sure what to get.

This is what my specs are:

CPU: Intel E8400
MB: Intel Extreme DP45SG
Memory: Corsair XMS3 4GB DDR3 2X2GB 1333
Power: OCZ ModXStream Pro 700W
HD: Western Digital Caviar Black 640GB


Thanks in adavance for the input.