I had a chance to play with the 85mm 1.2 II in low light on my 1D3. That combo really got focus with the rare front focus/no DOF problem I normally got. I have been told that the sensor site is smaller for focusing so critical focus is needed (the bride's eyes when coming down the aisle in a dark setting, for example) with the 1D/1Ds3 bodies. I have also been told that the center point focus assumption on a horizontal plane part of the algorithm for finding focus on the 1Ds2 was not incorporated in the 3 series bodies. I have no way to verify this but if these factors are true then absolutely accurate focus with a single focus point with 2 or 19 points assist would be required. Sooooo, that is what I do and I still get soft focus shots when the bride comes down the aisle (low light, low contrast). Looking over similar images taken with my 1Ds2 show similar tendencies and a similar number of soft shots, just not as bad as with the new 3 series bodies. That said, the best IQ I have gotten from any chip comes from the 1D/1Ds3 bodies. The files also seem to be better processing in LR. These bodies are keepers until something better comes along.
The first tests that I shall do on the new whatever-it-is-named "1D/1Ds4" will be in low light/low contrast settings. This HAS to be improved or the camera goes back.
FWIW, shooting fast and close motor sports (outdoors, bright sun) with a high S/N 1D3 and the 24-105/4 & 70-200/2.8 IS, I get spectacularly sharp files. Nearly 100% keepers.
Stu