Power required depends a good deal on the sensitivity of the loudspeaker being used. (Altec’s highly sensitive/efficient speakers at 60+5 watts likely produce more acoustic energy than my loudspeakers powered at 200+ watts per channel.) Example: if your L/C/R speakers are about 90db at one watt, and your surround speakers are 87db at one watt, that’s like having identical speakers all around but cutting the power sent to the surrounds by half. So, if you already know the speakers you’ll be using, compare their sensitivities before deciding on needed watts.

Another factor in deciding watts per channel would be if and how you plan to use subwoofers. If subs are going to carry all the burden of the lower frequencies full-time, then 300wpc for front L/R is not likely necessary. If your L/R speakers are going to perform without one or more subs for the lower bass, then 300wpc for low-sensitivity speakers may be a consideration.

As you likely know, some folks that want to give low power to some speakers and high power to others just use different amps.