As a former Solo X 12 owner let me jump in here and say that with certainty, they will not take 5k RMS each. Mine smoked in 30s on 5k of my Warhorse. My box was gigantic, otherwise they will take 2500w each clean. I repeat, they never have been capable of 5k each on the 12s and once the proper surround SPAIRS came out, they were actually re-rated to 1500w RMS and not 2500w.
The 18s (which were a larger coil and a monstrous motor) were changed from 5k RMS to 3500w RMS. The new figures were much more accurate.
If rebuilt by a proper sub builder w/ good soft parts, I would assume Ronal, Dave, Dean or the likes could make the 10/12 motors a 3k RMS sub and the 18 motors a 4k-4500w RMS sub. With OEM softs, there's no way.