Recently I was off testing three cameras:
Nikon D300
Olympus E-510
Sony A350

So I decided to take the same image of the same scene, pull the red channel for the mono conversion and compare the results.

Nikon D300
Nikon D300 Infrared

Olympus E-510
Olympus E-510 Infrared

Sony A350
Sony a350 infrared

Here are 100% sections from the middle of the images.

Nikon D300
Nikon D300 Infrared 100%

Olympus E-510
Olympus E-510 Infrared 100%

Sony A350
Sony a350 infrared 100%

Now all three look pretty damn good to me. See the individual infrared digital camera tests on DIMi of full details of each camera in infrared.