If i ain't mistaken, RMS power is just the capability of the voice coil to take in the amount of heat produced by the increased power, the better the capability of the voice coil to dissipate the heat, the higher the RMS rating, but u might be wrong though

There's not many ppl who would invest in machines that actually measure RMS power(if not mistaken, it doesn't even exist, the value is taken into play by calculation), as well, we don't listen to sine waves all day long, we listen to music, which fluctuates in terms of power being sent to the speakers, so... there's no FIXED value at all.

Testing of the DCR kinda serves no point, any multimeter that's accurate enough would be able to get the DCR.