well I do know me i7 4770k was enough for running 5 clients without any gpu, but that was the max I think now that I'm thinking about it
I would wait for Skylake cpu to come out , It seems to be quiet impressive or will at least lower the cost of haswell/devels canyon and is out end of this or start of next month I think. Or if you want more power again go for a E range cpu the 5820k is a decent chip but make sure and get a decent Mobo that can let you do all you need because it has less lanes than the 5930 and up and most of the budget x99 boards do not add onboard support to make up for this. for 15 clients I would go for a dedicated gpu, wow used to be mainly heavy on the cpu but ever since maybe mop it started using gfx a decent bit aswell, Someone better than me might be able to tell you when but i seem to remember a patch being released around the start of mop to make better use of gpu power. But it may well be the case when windows 10 comes out with the promise of direct-x 12 baked into the os with direct hardware access enabling you to share gpu cards with out using xfire or sli but running as bank of gpu resources available to windows you might find you can stack some older gfx cards. But I have not tried anything like that so not sure if that will still apply when running a game in direct-x 9, I have seen some tests in Win 10 builds that suggest it well may be the case but also seen others where it wouldn't work. So I think you might be safer holding off until skylake and windows 10 are released and see the lay of the land then. worth the wait imo for the sake of 6-8 weeks unless ofc they get pushed back by there respective creators.
