Saturation is the definition in which headroom is lost. This is the point where the circuitry is at user maximum and any attempt to go beyond this point will result in a clipped waveform at the output.
Now, as for your 4 Ohm rating in RMS>
One can extrapolate that since you have an RMS (root mean square) rating of 175 into 8 and no 4ohm rating at RMS, then you can look at the peak power rating and extrapolate the percentage -10% of that percentage to be safe. Saturation also reads as a continuous measurement as well of a sine wave as hardly only a 12.5% increase in power on instantanious peaks would be an accurate measurement of say a 10mS burst...where many amplifiers enjoy a 50% headroom allowment.
Just to throw a figure out to you..and this by no means scientific and based on the information you provided..
I would safely say that in 4 OHMS, your amplifier can produce a good RMS of 260 watts.
Saturation is the point (depending on design) where the combination of power transformer/Power supply, Output transistors and heat build-up is at maximum. Saturation or "soaking" is usually referred to as a longer duration than a simple burst. I would be keen to know what that duration and bandwidth is for those figures supplied as the "saturation point" At 1khZ, power is higher at saturation in most designs than full power bandwidth.
