The SF is a 4 Ohm load, rated 91 dB Sensitivity. To convert to Efficiency, which is a more useful spec for tube amplifiers, you have to subtract 3dB on account of the fact that Sensitivity is a voltage measurement, while Efficiency is power. 2.83 Volts into 4 Ohms is 2 Watts and the Efficiency spec is 1 Watt/1 meter. Thus we arrive at 89 dB.
I don't think the M-60 can make enough power in a room of that size, even when using the ZERO autoformers to correct for the impedance (and also results in more power, about 80 W/channel).
IME, having used speakers of that efficiency in a room of similar size, I found 200 Watts to be more satisfying. You have several options; if you get the M-60s and keep the SF loudspeakers, you want a set of ZEROs and you'll be living with occasionally overloading the amps.
Or you could get a more efficient loudspeaker. Some good suggestions are on this thread (I don't think the older Quads would be good since they are not all that efficient).
Or you could get an amp with more power for the SFs. If you go this route, FWIW our class D amplifier sounds a lot like our M-60s and has no problem driving 4 Ohms with considerably more power.