Update: GET is working fine for me. Great work.
Have you had a chance to look at the updated phatk kernel from 7-17? It would require interface changes between cgminer and the kernel, but it's the smallest kernel (least AUOPs) yet.
I suspect the timeout is just too long with the GET so that even if it works it's eventually reset. I'll change that shortly in my git tree.
Yes I've experimented with the updated phatk kernel and haven't been able to demonstrate any measurable advantage :s Nonetheless I'll eventually implement it.