ATI Radeon HD 4870 running in CrossFire with Phenom II X4 940
 

F.E.A.R

In this test, the game is run in 1600x1200 mode with computer set to High. In Single 4870 card mode, it scored an average score of 185 fps. With crossfire enabled, the score shoots up to 310 fps. A 67.5% jump is recorded for this test.

CrossFire mode

Call of Juarez

in Single card mode, it scored 42.7 fps. The score 42.9 fps is recorded when running it in CrossFire mode. Seems that CF doesn't help much in this game. Just a side note, the CoJ benchmark sometimes do give a boost but sometimes don't.

CrossFire mode

Crysis Demo with single 4870

The settings used in this test is 1600x1200 No AA DX10 test. Using the HOC Benchmark, the overall quality is set to High. With a single 4870, the benchmark scored 33.92 fps on the average.

With CrossFire enabled, the average frame rate dropped to 31.7fps instead. One thing to note is that the lowest and max frame rate in the test is higher than that of the single card.

Crysis Demo with 4870 in Crossfire

Here is a summary of the results

It seems that other than F.E.A.R and synthetic benchmarks like 3Dmark06 or 3DMark Vantage. CrossFire on the CoJ and Crysis did not bring much of a difference to the performance of the game. This can be confirmed as we do not have a GPU limited situation here.