How much extra graphics horsepower do 3 monitors need as opposed to 1?

[tom thumb]

Originally I thought that with 3 monitors, you need 3x the power (let' s say 5870 = 3x 5750), but benchmarks say otherwise.

With an eyefinity setup, how does the necessary hardware scale with # of monitors?

Also, If I want to future-proof for gaming at 1920x1200 with 1 monitor, is a 5770 enough? If I have 3, will I be able to get by with a 5850?

Thanks!

 

[mister g]

Future proofing with a 5770 is not smart at that res, go for the 5850, go for 5870 if you want 2 more monitors.