I get artifacts playing 5x WoWs only if my computer hasn't been rebooted in a little while after I've already 5 boxed. (ie: I 5 box yesterday, don't reboot, then this morning play 5 WoWs, I will almost 100% get a ton of artifacts to the point where I have to hard exit and reboot). I personally feel it is a memory related issue, but I can't really put my finger on exactly what causes it.