Power in watts vs volume knob position is not linear - it is exponential (since human hearing is logarithmic). When you set volume pot at 50% of the peak volume position amp will produce 10% of max power (1/2 of volume = 1/10 of power). Assuming 100/125 ratio of power is equivalent to about 94% of the volume* it will be very close to max power position, but we usually don't know what it is. Probably most of amps have max volume between 1 and 3 o'clock position of the volume knob to provide additional gain for softer than nominal sources/recordings. I agree with Elizabeth - 600W would possibly be a problem, but you would hear huge distortion before burning down the speakers. Slightly larger amp's power rating is even healthy since most of the speaker damage is done by underpowered amps that clip when overdriven. Clipped signal has a lot of harmonics and tends to damage the tweeters, that are not designed to handle it.
* Perceived loudness = k^(1/3.5) where k is the ratio of power.
* Perceived loudness = k^(1/3.5) where k is the ratio of power.