I'm running 7.1 Update 3 on my Color Classic (just got it running two days ago) - 7.1 will need system enabler 401 as I learned.
Another option for managing multiple system folders is to use System Picker, allows you to bless different folders. Eg install System 7.1, then rename it to "System 7.1" and install 7.5, rename it to "System 7.5" and use System Picker to reboot between the two/three/etc
If that relates to power consumption, then its entirely possible. Unless we have internal apple documentation, then we have no way of knowing, unless you know how to do certain experiments?
Regardless, ive used them interchangeably and luckily have had no ill-effects as of yet.