Well, Windows 8.1 is a huge difference, there isn't much else aside from that--memory amount, bandwidth, and PCI-E bandwidth are irrelevant in this case or would have a non-existent affect on performance. The GTX 770 is the same gk-104 in the 690 and the Xeon E3-1270 you have is comparable in terms of performance to mine (especially if it is not overclocked). The other main variable would be server pop...

May I request that you disable vsync and the fps cap, as well as comparing your fps with occlusion culling on/off and attempt the process again? If there is any significant change in fps the issue is present, just not as severe.

The performance hit mainly happens in certain hotspots, so you would want to be in roughly the same place and facing the same direction as I was in the screenshots--if you look directly at the market board, or face to the opposite side of the retainers, the performance hit isn't anywhere as severe or is simply not there, respectively.