I've been hesitant to open it up as I can't see why just overclocking it would be a hardware issue, and I might be selling it, should I ?
It could indeed be a hardware issue since most of the times these heatsinks are loose, affecting cooling (bad cooling equals less headroom for OC'ing). Also, some cards being not seated well can also affect cooling, same result. Lastly, not fully seated cards can have poor connections with all sorts of problems leading to poor OCability (heat, electrical noise, etc).
So, yes, open it. Carefully tighten all heatsink screws and seat the cards well and evenly, and then carefully reassemble (the LED and USB connector have to be watched closely when putting the face plate on).
If that doesn't fix your OC problems, be sure the ambient temperature is not too warm and you have good airflow around the devices AND that your powersupply is not the problem (numbers aren't the full story here, also has to do with the surge control, the rail stability, etc).
Thanks, I just opened up the front and the majority of the cards were not seated evenly in the bottom connectors or top rails ... I pushed each one down into their positions far more squarely. I also noticed when I opened it that the main board they all sit on it bent down in the middle as if pressure has been applied too hard from the top, anyone else notice this?
Even so after pushing all cards better into their fittings and retrying in high clock mode I only very briefly got this before getting another completely x'd out reading:
ASIC_01-16: x x x x x x x x x x x x x x x x
ASIC_17-32: x x x x x x x x x x x x x x x x
ASIC_33-48: x x x x x x x O x x x x x O x x
ASIC_49-64: x O x O x x x x x x x x O O x x
ASIC_65-80: x O x x O x x x x x O O O O O O
ASIC_81-96: x x x x x x x x x x x x x x x x
M_01-16: 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000
M_17-32: 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000
M_33-48: 000 000 000 000 000 000 000 000 000 000 000 000 000 798 000 000
M_49-64: 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000
M_65-80: 000 000 000 000 000 000 000 000 000 000 000 000 399 000 000 000
M_81-96: 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000
Jobs:0000000056 Accepted:0000000003 Rejected:0000000000 (0:0) F1 F2 F3
MHS:01197 Utility:016 Efficieny:005.35%
It still works in low mode though ...
Where exactly are the heatsinks?