How much power for Merlin VSM speakers?


I bought a pair of Merlin VSM-MMs and am driving them with a Cary SS amp. While it sounds pretty good I am thinking of switching to a tube amp. I am familiar with the usual OTL suspects most people use like the Berning and Joule. I was wondering if there is anyone out there driving these speaker with a less powerful SET amp. How powerful does the amp have to be in order to not clip? Is the speaker efficient enough and its impedence curve benign enough for low powered amps? Is 30 watts enough? Am I asking the right questions?
abrahavt
At one point, I ran my VSM Milleniums with a WAVAC 572 SET, certainly not your classic flea-power SET, it put out about 50 watts. I seem to recall seeing threads here or on Audio Asylum where people used lower powered amps on VSM's, but I can't remember for certain, so no link.
in a 12x20x9 ft room my 18wpc wellborne amps were excellent. now i have a 14x30x10ft room and i likely need atleast 150wpc.