From what I see on the web, it appears the answer appears to be #3 below, limited by the application. I'm reading the same issue is being seen across many platforms.
One other item to note is that the beta version of this application appears to limit multi-core use, so be sure to use a full version for best performance.
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seems like the program isn't really needing all that processing power.
You could try and run the game, ALT TAB back to windows, open Task manager, find the game executable process in the processes tab, right click and select Set Afinity. uncheck all but the first 4 CPUs (0 - 3). go back to the game, play for a minute or two and then come back to see the processor utilization.
Ok, thanks, I was thinking that it was the program itself, I just wanted to double check and see if their was any other factors that could be limiting it. It seems that while the program is multithreaded, you really have to press it to turn it on, simply setting affinity in the task manager isn't enough, You have to press Ctrl-alt-C several times (not just once) for it to notice that it can use more than one core.