Single 5850 or Dual 5750?

It really depends. In some games the 5850 is faster; others, dual 5750's are faster... and in some games it's a wash.

Some important questions need to be asked in order to make a more informed decision. What size monitor are you planning on using? What PSU do you have?

If you're not going to use at least 1920x1080, then both choices would be money spent needlessly as a single 5770 would do just fine. Also, dual 5750's would require a heavier PSU: one with at least 55 amps on the +12 volt rail.

Radeon HD 5750 review (Crossfire)

SlackerITGuy said:

I'd go for the single Radeon HD 5850.

MultiGPU solutions are not the best way to go right now IMO (micro-stutter, games not 100% optimized for it, min FPS issues, etc).

Don't forget heat either.

~Lordbob

The 5750 is exactly half of a 5850 in every way. If you crossfire, you won't get double the performance. At best you will get 80% better. Also when running in crossfire, you only use the memory capacity of a single card so 2 1GB cards will perform as if they had 1GB of memory. In general its best to use a single card whenever possible to allow for upgrades in the future and a single card tends to yield better performance too. A Guy

Single 5850 is a better choice - Crossfire is simply a PITA the majority of the time.