The benchmark itself seems to only use 2 cores. We have two systems here, one 2700k @ 3.9GHz with a Radeon 6970 @ 905/1425 and another Q6600 @ 3GHz with a Geforce GTX 570 stock. Gives a good comparison as both systems have about the same GPU performance, but with a large CPU performance difference. In the benchmark at, the 2700k system easily beats the Q6600 (6200 VS 4200 @ 1080p Max).
Monitoring CPU usage during the benchmark shows the 2700k (with HT on) peaks at 27% load, and the Q6600 peaks at 57% load. The numbers clearly shows two full cores being used with idle background tasks taking up the rest. So, in the benchmark all your need is CPU frequency with a reasonable GPU for a good score. Extra CPU cores don't help.
In the actual game, CPU usage is much higher. I've only tested it on the 2700k system so far. The game is very playable at 2560*1440 on maximum, but I've seen CPU usage maintain ~42% (with the odd spike around 47%) on a number of occasions once you have a large number of player characters on screens (FATE events and towns usually cause this). Frame rates remain good, but it's clear the game when running in real time is able to max out 3 cores quite easily, and is maybe offloading threads to more cores too.
Anything from an i5 2500k upwards should easily provide a solid playable experience even without overclocking, albeit without a solid 60Hz lock. I've never seen anything I'd call questionable performance on my i7 2700k @ 1440p even in the most demanding areas so far. AMD users probably want to be aiming for a PII-X3/FX-6000 series or higher as a minimum for the game given how threaded it is in real time.