I'm on the same boat. I currently have a i7 920 @ 3.6GHz (MHz lol) ; G.SKILL F3-12800CL6T2-12GBPIS (2Gx6); Radeon HD5870, on an ASUS P6X58D-E also a Samsung 512GB 830 series for the OS.
Even though work and desktop usage is fast enough I really feel the performance hit in ArmA2:CO and SPECIALLY ArmA3. This is actually how I currently evaluate my systems and builds—since it's a great part of my gaming.
ArmA is a hog when in comes to performance, it really taxes the CPU ( well, GPU as well but specially the CPU); sometimes even more than Metro Last Light/Crysis—the engine is huge and it's not fully optimized. What really matters to me is the online component anyway; the synthetic benchmarks are useless.
Reading this thread I figured I will wait; maybe Skylake will be a better option for us? So, I guess I'll go for the new GTX 780; even though I know for a fact it will still tank on big battles and large AOs, the power of a 780 can't hurt, right?
It's still better than upgrading the whole system; besides, I'd really get those CUDA cores some decent usage~I so wish Adobe would support opengl for good