I think the R9 280X is perhaps even better than the HD 7970. It has just a tiny bit less GFlop power, but runs far cooler (tdp is 190 Watt as opposed to the 247 Watt of the HD 7970), other features (ROPS, TMUs, SIMDs) are the same, so more room for overclocking. It starts with a core clock of 850MHz where the HD 7970 starts with 1000 or 1050, depending on the model. Cranking the R9 280X's core up to 1050MHz will see it perform just as good as the HD 7970.