According to the reviews, 290x is a mixed bag, depending on subjective definition of "performance". 290X is definitely billed higher-end than 770, since it beat even Titan in initial reviews. However, it turned out that 290X in current launching configuration has serious inconsistency issue with very very loud noise and thermal throttling. Until boardpartners will launch with customized cooler, you have to evaluate such pros and cons yourself. When it happens, I think definitely 290X will beat 770 in every aspect for sure, in terms of performance.