I think Outlaws response to this issue is accurate enough. What is the issue? Do you think the 750/755/770 will not actually deliver their rated power?
P=V^2/2R
Power is RMS, volts are peak and R is in ohms. Buy my hand the 750 delivers 51.3 volts peak into an 8 ohm load. Peak current is 6.4A. All 5 channels driven gives you 32A peak. Peak volts times peak amps give you peak power; 1644W. I believe that I read that the 750 has a 1650 VA transformer. Judging from the 4 ohm performance this is conservative.
The 750 delivers 44.7 volts peak, 11.2 Amps into 4 ohms; all channels driven for a total of 2500 W peak. If it can do this and not catch fire I think we're OK. I don't think fire has been a big issue, at least with the 750.
Hopefully the material you listen to has an average 50% duty cycle, DC just doesn't sound that interesting. If the amps are 50% efficient and considering 50% duty cycle the VA ratings make sense.
IMHO unless the amps don't deliver on their spec this is a moot issue. Wait for a test if you really doubt Outlaws ratings on the 755/770. I'm sure the 750 was tested; did it not deliver full power?