I honestly don't know what it is mate and I'm at my wits end. Before the last "patch" a couple of week's ago it was running seamlessly (other than the inherent hit reg and "netcode" woes that everyone bangs on about) and then BAM - got completely done over. Trying not to be the whinging type I looked at my own gear first, hence the wipe and upgrade of the OS and while it's improved it's still nowhere near where it was
I also reset everything back to it's absolute default (stock clock, memory timings, gpu clock and memory speed etc) when I did my clean install and still no avail. Tried both the beta and the 13.12 stable drivers. My BIOS and chipsets are all up to date and I even replugged everything back in just to be absolutely sure so I am done! haha