GameGPU has the charts you're looking for:
http://gamegpu.com/action-/-fps-/-tps/arma-iii-test-gpu.html
Their testing suggests this game only heavily uses 1 thread, so the i7 would offer basically no benefit. Even a fast i3 would perform about the same, but any Intel CPU would be far faster than an AMD CPU.
Their review is quite old and doesn't include the latest Intel CPUs, but the overall message is that you want the highest clocked, latest Intel CPU you can get, and core count is irrelevant:
An i3 6xxx would be around as fast as any stock i5 or i7, but an overclocked i5 6600K or i7 6700k might get you as much as 25% more performance. If you consider 25% worth the extra cost of an i5 6600K + Z170 motherboard, over an i3 6100 + B150 motherboard, go for the i5. That's a lot of extra cost though, and I think the i3 would be a good choice.