Not really. Especially for comparison reasons. The RMS rating is simply a thermal rating of how much power the voice coil can dissipate before thermal breakdown, that is it. The only time it is remotely meaningful is in the modeling process to ensure you don't design a enclosure that is so inefficient that you reach the thermal barriers of the driver before you can reach full linear excursion within your usable pass-band. It also has absolutely nothing to do with "how loud" a subwoofer will get under ANY circumstances. Of all the T/S parameters, it is one of the least important when choosing a driver...