http://imgur.com/VSLvV5o
Yeah... Not sure why you're getting full pool speed and I'm not. I'm using quad core processors as well. CPU utilization never is more then 2-5%. I'm using 970s, what cards are are you using? I don't feel as though this is a card bug though...
I'm also on W8.1 x64... However that shouldn't make a difference as this seems to be some sort of networking issue... That's release #4 right?
Maybe you guys could help me figure this out. I have one rig where the MCU while mining Eth never hits 100% on 3 of the 6 cards. This means they're mining at about 10% less hashrate then they should be, give or take. Processor isn't being maxed, overclocks are fine, TDP is at max as is temps, I really have no idea what's going on with them. I even changed out the mainboard and that didn't do anything.