I tied my cluster of 7950 to P2Pool and was getting tons of HW errors as well but then pointed it to the litecoin client for solo mining and recieved none. I am hashing at 700KHash on all my cards but am a little paranoid that they are getting HW errors. None are showing up in cgminer and I have it set to intensity 20 with no issues. I will try downgrading as well and see if that works better with the P2Pool though.