Thanks, I did read through the thread. It appears they are having better performance with speedlight AF assist. A few mentioned some various little tweaks that helped them out in specific situations, but I wasn't able to find any that made a large impact on the sensitivity. If there is enough light, then the 5D3 is faster in servo mode than in single shot. Single shot mode is a bit more sensitive in low light. Once the lights are dimmed enough to cause servo mode to hunt, I can switch it to single shot and still get a lock. However, if I continue dimming the lights and get to the point where the 5D3 hunts in single shot mode, I can still use the D800 in single shot or even in it's own AF-C servo type mode. So as the lights go down it goes from 5D3 servo, 5D3 single shot, D800 AF-C, D800 single shot. I think the 5D3 deserved whatever center point they tossed into the 6D.