BillFitzmaurice.info

What ive gathered is that
1, We use a sine wave to set voltage limits
2, We dont connect the speakers during limit setting

Result
1, Music is far from a pure sine wave- extra protection
2, You can hook up a dummy load but if you dont - more protection

I was concerned about the dummy load as well and loosing that couple of volts but have come to terms with the fact that if at 50v its not loud enough I need more cabs and I like the idea of extra protection.

Your question has validity though, im sure there's alot of "science" to it and it can be answered better but truth be told its marginal gains to be had.

Don't forget that Volts x Amps = Watts. The amplifier will only flow a certain amount of amperes, after which the voltage will sag. Limiting voltage should mean that you will not encounter sag. If it does, then get a more powerful/better amp.

Tim,
There is no difference between 1 and 2.
If the limiter is outboard like a Driverack, or the limiter is onboard like some of the newer Crown amps etc, in either case the limiter is before the amp.
In the second case the limiter just happens to be in the same box.

The "sag" you're discussing in amps is a combination of factors.
If you could find a high power amp that had a perfectly linear output and a power supply that could keep up regardless of load, you wouldn't see that sag.
However, a smarter man than me, Mr Einstein, said “Energy cannot be created or destroyed, it can only be changed from one form to another.”
Since amplifiers create heat, that tells me that energy input from the power supply is "lost", therefore no amplifier can be 100% efficient. The lower the load, the greater the heat generated. And we see the sag.
Much less the power supplies ability to give the amp circuitry the juice it requires...