Couple of things:
Hyperextend = injury. Overextend is the word you're looking for. Unless you're telling me you have the ability to injure your back through overextension. In which case, don't do that.
If you OVERextend your lumbar, the pelvis tilts further ANTERIOR, not posterior. Right?
I think your stance is wide. Bu the angle and lighting are bad for determining that.
Finally, watch rep 3 and tell me what it had in common with reps 1-2, and not in common with 4 and 5.
This set was hard because of reps 1-3.
Finally, what's the deal with your DL? Why is it only 5# ahead of your squat at this point? I think some answers lie there as well.