I think the problem is the lack of support for the GTX 660 and other 600 series cards so there isn’t alot I can do about it.
I’ve managed to get things to work for now by turning off GPU acceleration when I’m editing and turning it back on when I’m ready to render, it does make the process a bit longer though with the CPU having to do all the work. I’ve got an I5 4690K and it’s being pushed to 100% usage when playing from the timeline so I’m not too happy about that but I’ll live with it.