Auto Focus Speed & Acquisition | 5D Mark III

[Mark Elberson]

A while back there was a thread about f/2.8 cross type points and how there was no benefit to auto focus speed when using faster than f/2.8 glass due to the contraints of the auto focus sensor itself. My 5DIII has many f/4 cross type points am I am wondering if it works under those same constraints? Simply put, should I see a difference in auto focusing speed when using faster than f/4 glass? My 24-105 f/4 has been hunting in low light and was wondering if it was worth my while to throw on some faster glass to speed things up.

For this dicussion I am not interested in the differences in accuracy.