To the nekked eye, you'd say there's no difference in-between the two cards. Focus on the PCB a little and notice that there are some design changes. The card on top is the Radeon HD 4890, the lower card the Raderon HD 4870. Focus on the capacitors and you'll spot the difference.

Once we flip both cards around things become more apparent, this definitely is a different PCB. Look at the green sticker on the lower HD 4870, focus on the resistors etc and then compare to the upper card.

And there she is, doing a good workout in our test-lab. All sweaty and steamy hot... hmmm. Alright, we just installed the card. Let's have a peek at heat levels, power consumption and see how noisy the cooler is.