HD4850's vs. 9800GTX/GTX+'s

hi all, i just sold a 9800gt on ebay and got 125 for it so now im looking to spend up to $50 on a gpu. now ive heard and seen that the HD4850=9800GTX/9800GTX+ (please correct if im wrong) , so my question is which one of these cards would fit me best?

system that gpu will go into is as follows:

E8400@3.0GHZ (no oc yet)
2 GB Ram@800MHz (adding 1GB when i order gpu)
500 watt psu
19" lcd monitor (1440x900 resolution)
Gigabyte EP43-DS3L Mobo

and here are the cards im looking at (note, i have never used an ati card before. *im not a fanboy* its just ive never had problems with my nvidia cards. but since ive never owned ati before idk if ill ever have problems with those will i?)

Radeon HD4850's:
http://www.newegg.com/Product/Prod [...] 6814102770
http://www.newegg.com/Product/Prod [...] 6814125238

9800GTX's:
http://www.newegg.com/Product/Prod [...] 6814130339
http://www.newegg.com/Product/Prod [...] 6814130403 (would only cost me about $5-10 out of pocket)***

9800GTX+'s:
http://www.newegg.com/Product/Prod [...] 6814130376
http://www.newegg.com/Product/Prod [...] 6814150314

i know it depends on what games it will be used for, but the pc its going in is a secondary pc (although its my first build) but the games are crysis (of course) COD4 (again WOW) and Grid. also looking into spiderman web of shadows when that hits but thats not a graphically demanding series of games we all know. so thanks for any suggestions in advanced, im really leaning towards the EVGA 9800GTX recertified because its the cheapest and i can just oc it to match a GTX+ easily and because of the step-up program EVGA has.

thats what i was leaning towards. thats what i did with my GTX260 Core216 is i bought the reference card and matched the superclocked editions clocks so i have a superclocked core 216 for a reference core 216 price. so ill get the EVGA 9800GTX and oc it to match the GTX+ to save some cash again. thanx dagger for input. still would like to hear from more of the toms community also.

All three are good options. The Sapphire HD 4850 would get my vote. If your mobo was an SLI one I may have said one of the 9800's. (the new evga 9800GTX or the XFX 9800GTX+).