I just found some good deals on craigslist for both cards, but here's the breakdown:
Radeon HD 4850 512 MB includes a Zalman VF900 cooler fan worth around $30-40, and I can get both for $37.
Radeon HD 4870 512 MB GDDR5 doesn't include anything extra but it's a little better statistically than the 4850.. however, the seller is selling at $50.
Would a ~$10 difference be worth the money, plus it won't come with that sweet cooler fan? Please note: I only play Call of Duty: Black Ops 2, so I just want something better than my crappy HD 5450, lol. I'm not a hardcore gamer though.
Also the HD 4870 consumes 40 more watts of power (150 W), and I have a 300W PSU.... really not optimal for either card but I hear that it can at least run the HD 6770 with no problems, and that card takes up the same power as the 4850 (110 W). Would I just go with the 4850 since it'd be safer to run, plus it's got a fan on it?