If everything is set to manual, then the camera isn't metering anything. The only time metering would come into play is when you're in an AV, TV, or auto ISO mode and the camera is deciding what settings to choose. If everything is on manual, then you are doing the metering not the camera. Am I missing something?
If you do want to test how the cameras each meter (and that is a valid question) you need to put them both in the same auto mode and shoot with identical focus points. When you do that you'll see the 5D3 and 1DX behave quite differently, specifically because of the focal point-weighted metering on the 1DX.
I'm lost. The camera meters out of the same point on both cameras. The 1DX only meters out of a focus point on spot metering. I didn't use spot metering, I used center weighted average. Second point I'm lost on, is that when the camera tells me it's properly exposed (the meter on the right hand side on 1DX and bottom on 5D3) the brightness is different on each camera. 0 EV on 1DX is different than 0 EV on 5D Mark III. This is a very simple test. You can shoot in auto ISO at 1/100, f/8, and get ISO 6400 on the 5D3 and ISO 5000 on the 1DX. That is very similar. However, upon inspection of the photos, the exposure is brighter on the 5D3. Well of course, it's ISO is higher. The point is that it gave correct exposure at a brighter image than the 1DX did. Again, a very simple thing.
And I don't know why people can't understand that AF-point metering is for spot metering. CWA comes out of the CENTER. It doesn't matter which camera you are using. Besides, why is it so hard to understand that I used the center AF point anyways in all of my shots?
I cannot explain this again, so I'm sorry if I'm not being clear.