Unfortunately, right now the game is not greatly optimized and will thus run quite bad when a large amount of assets is in play, even on high end hardware. Most of this is felt by everybody, even a high end rig will meet problems when it is presented with, for example, 10 planes sitting on the ramp trying to do their thing to get into the air (in multiplayer).
DCS World 2.0, which is to be expected to be released soon, will incorperate support for DX 11 (as long as the hardware supports it, which yours definitely does), whilst DCS World (1.0 , current version) has support for DX 9 IIRC. Aside, I believe we will also see some optimalization, but don't quote me on that.
Some info about this can be found in the DCS 2.0 thread
http://forums.eagle.ru/showthread.php?t=135473
Whilst some other info, regarding the optimazation and the GPU support can be found in the last Q&A video. Skip to around the 7 minute marker.