A dual processor twelve core server?

Well, the single core speed is well above the 3 GHz line Skuzzy once recommended, so that won't cause a bottleneck. The number of cores also allows for assigning background processes to other cores than those used by the game. However, you most likely won't see any difference compared to the i7-2600, they're both overkill for AH. So is the amount of RAM.
As Spikes said, the R9-280 is not the best but it almost doubles the benchmark scores of the one I use so it's quite good a performer for single monitor use.
What concerns me most is the power supply. If that's a server like it seems, what kind of a power supply do you have? The R9-280 needs a 8+6 pin dedicated power cord to run.