Verified answer

OEM is just what computer makers/manufacturers use.

OEM products:

OEM products are exactly the same as what you would get in a shop, shop's sell Retail packed products, so if you bought a retail packed version of windows you would get a case for the disc and usually 3 licence keys, OEM you get a sticker and a disc only (if you buy it yourself) and it's only 1 machine activation, so computer makers use it becuase it's cheaper.

oem Components are exactly the same thing, an OEM graphics card is exactly the same as the retail version, the only diffrence being you dont get a box, drivers disc, manual, cables or stickers.

i usually buy OEM when i get computer parts because there cheaper, there the exact same thing as retail, only without the flashy packaging and extra's that you don't really need.

Edit_

the card will have the exact same clock speeds and memory speeds/amount and everything as a retail version of the card.

http://www.techpowerup.com/gpuz/

(scroll down to the bottom to download)

will tell you information about the cards clock speeds and stuff.

if the speeds are lower, it's probably the power saving features of the card, ATI lower the clock speeds when the graphics card isnt needed to do intensive stuff. you can check the full speed if you start a game with GPU-Z running and then check the sensor tab (keep the sensor tab open when playing a game)

remember to keep your drivers upto date! it makes a diffrence in game.