Last year, Sound & Vision magazine did a bench test of the Onkyo 900, one step below the 797ver2. Rated at 125 wpc x 7, testing revealed it only capable of 54 wpc. Conversely, tests done on NAD receivers showed they were conservatively rated by NAD--they actually exceeded their stated power by 15% or more. Furthermore, the quality of the parts put into the NADs put Onkyo to shame. NADs appear to have much better power supplies, DACs, DSP, and output transistors.
Not comparing high end, but I did get to directly compare a bottom of the line NAD 742 last year with an Onkyo 700. Now the NAD was rated at 50 wpc and had an MSRP of $649 and the 700 was rated at 100 wpc and had an MSRP of $799 or $899, I can't remember which. The NAD totally embarrassed the Onkyo in both music and DVD playback. With CDs, the sound was more focused, with a better soundstage and more dynamic sound. Each instrument was clearly heard with the NAD. With DVDs, I was surprised that I heard things like background noises or conversations clearly through the NAD that were either muffled or didn't even exist with the Onkyo (note, this was using the same speakers and the same source material, and the receivers were volume matched). All in all, the NAD was clearly a better receiver.