no, high RMS means that the voice coil can handle more watts without overheating/burning. Mechanical limit(xmech) depends on the enclosure, source played and the driver itself.My understanding is that with higher RMS means the cone can take more power before distortion/breakup.
Then coupled with more Xmax will give you higher SPLs.
So the higher the Sensitivity,
greater the RMS,
and the geater the Xmax,
should = higher SPLs
With my experience, low sensivity subs needs more power but sounds better IMO, you tend to have more headroom, volume play, but thats just a feeling you get I guess about low sens subs... high sensivity subs are a lot easier to run powerwise, but reaches their xmax and xmech quicker(not saying it doesnt sound good at all) ...
high xmax and xmech:
Also, a high xmax sub sounds better , you get lot more headroom, subs with lot of excursion has more playground to play with, thus the sound tend to be more confortable to the ear IMO, more "round" and cleaner....