The more useful chart is this comparing the CPUs:
Here we can see a very slight advantage to the 6 cores but its really not worth talking about. However this is in a single player environment in the middle of beta when everyone in tier1 agreed they seemed to have broken the engine from the alpha to the beta. They have now fixed it again for release and its back to scaling a bit better and running a lot better than it did during the beta.
In multiplayer, in real games using all 6 cores is better than limiting the game to 4 cores. The average FPS is most of the time improved by around 15% and the minimum also. However that is SB-E compared to SB-E. That 15% will almost certainly be eroded by the difference in architecture that Haswell has compared to IB-E, certainly much of the advantage will be gone. Practically I don't think there is much point getting a 6 core for the game, the price/performance isn't worth it, but it is the fastest solution we know of (we run a heavily scripted highly modded version of the game, as I think do most Arma communities).
BIS have actually published quite a lot of details so to why they have this poor multithread usage and what they intend to do about it. But this is a problem they have been working on for years and its not easy to fix. Arma has one of the most advanced simulation engines ever made and its extremely complicated. They haven't yet found a nice way to utilise those additional threads for the AI (which is our biggest concern) or players for the server. They are working on a course grained threading approach but it likely wont work past a relatively small number of cores (4-6 I guess). Arma is a prime example of why so many games aren't multithreaded, its intrinsically difficult and it might be impossible (mathematically provable) to use multithreading fully in many games.
I really like the way Arma looks, its got a realistic lighting system that isn't over done or highly stylised. But it really does need a fast CPU and preferably an overclocked CPU to run well.