X-bit Labs has taken a look at the performance of the ATI Radeon HD 4830 in CrossFire, and compares it against the Radeon HD 4870 which costs about double as much as a single Radeon HD 4830. You can check it out over here.
Here’s the idea: a Radeon HD 4830 can now be bought in retail for slightly over $100 whereas a Radeon HD 4870 1024MB will cost you about $230 or more. Easy to see, there is a difference of $120 between the retail prices of Radeon HD 4870 and HD 4830. In other words, one HD 4870 costs as much as two HD 4830 cards (and you will even have some change to keep). And as you perhaps know, two Radeon HD 4830 can be joined together using CrossFireX technology and increase your computer’s performance in games. Or you can save on your graphics card today and buy a cheap Radeon HD 4830 and then buy one more such card after a while for even less money (due to inevitable price reduction). It would be more profitable than if you sell (or throw away) you existing card to replace it with a faster one.
The reviewer concludes a pair of Radeon HD 4830 graphics cards is generally faster than a single Radeon HD 4870, if you're willing to embrace the certain difficulties and problems of CrossFireX. A pair of Radeon HD 4830s also uses a lot more power.