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http://gpuboss.com/gpus/Radeon-R9-290X-vs-Radeon-HD-5770
About the best thing I could find and I hate this site

GPUBoss shows nothing and is totally rubbish.
The 5770 is a 2009 GPU comparing it to a R9-290X is like a bicycle vs a Ferrari![]()

It does show some useful stuff, such as:
"Much better 3DMark 11 graphics score 32,271 vs 2,410 Around 13.5x better 3DMark 11 graphics score"
Yeah you should see a big difference![]()
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.What would the Wright Brothers make of this?
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Two 5770s was about 10 percent faster than a 5870. I would say the 290x is about the same as CFX 5870 so you're talking four times the performance. As has been mentioned - astronomical.