Graphic card upgrade

I've got an early 2009 MacPro desktop with a 30" Apple monitor that i would love to be able to play some of the games on like the Call Of Duty series and the Medal of Honor series. Problem is my graphics card a Geforce 120 is to lame to run these programs. Would like to upgrade the card to something that will allow me to play some of these games.

I found an ATI Radeon HD5870 card that looks like it might work, but finding a driver seems like a problem, they all seem to be for a windows machine, nothing showing for OS X. So anyone got any ideas about if this card will work under El Capitan ? Or a suggestion about a different card that works under El Capitan ?

If you haven't done so already, have a look at any of the upgrades available for your Mac model at:
http://www.xlr8yourmac.com
and
http://www.everymac.com

The http://www.xlr8yourmac.com will be your best bet, especially if you're considering modding any windows cards etc.

Ok thanks for the references to check. After reading around i decided to yank the card out of an old windows machine that i used as a game player that had gone belly up. It is a Nvidia GeForce GTX 560 2048 MG card that i had used for quite a while that defiantly did a good job in the windows machine. All i had to do was get me a couple of power cables to hook the card to the MacPro and it works great. Didn't have to find a driver or anything, El Capitan knew it and it worked right off the bat.

Ya it's a windows card and i miss the first and last of the video on boot up and shut down...big deal i don't get to see the Apple icon or the slide bar on boot or the little round and round thingy on shut down... I think i can live with that as the rest of the time the card works just fine and i can now run the games now that i could not before.

Congratulations. That was a very easy & inexpensive solution!

- Nick