I use the PSB stratus line. In this case the mini speaker actually is less efficent than the Golds and require more power. So because the rears are smaller does not mean that they need less power.
Surrounds don't need as much power
I'm in the process of upgrading amps and wondering if the surrounds really need as much power as the mains and center channels. The speakers are smaller and there's less information going back there, it just seems logical that less power is really needed.