I agree that new CR123's should read more than 2.95v. That's what these particular brand new Duracells came out of the package at. But isn't that irrelevant to the issue here? Together they're still going to be well above the threshold value of 3.8v for the M60 module, but they produce less light than the higher voltage RCR123's.
I also tested it with new Titanium CR123's which read 3.1v ea. and got the same results.
This shouldn't be so surprising. Many of the multipower versions of different lights (e.g., DX Ultrafires) run brighter at higher voltages, even though they should be feeding the LED at a constant level.
Edit: I just retested w/ another pair of Titanium primaries @ 3.26v each. Same results, RCR123's were 10-12% brighter than CR123's.