Ive auditioned both of these fine speakers. IMO, it boils down to the best available synergy (or. lack of it …) with your upstream electronics., and personal bias of faves.
I would generally pick the HARBETHs ….BUT …( and it’s a big “ but”….) their sonic signature and class leading midrange excel with beefy Euro (especially British ) upstream electronics with their respective bespoke sonic signatures as stablemates to the HARBETHs . . Think robust Class A or Class AB amps and source here.
WPC specs alone are meaningless…it’s the “grunt” evidenced by an abundance of high-current (amps) that matters here. I would be very cautious and personally audition the HARBETHs first with their 6 ohm impedance and lowly 83db sensitivity / efficiency, …..and resist just blindly pairing them up to your NAD M2 class D amp with its comparative bespoke darker sonic signature.
System Synergy matters ….big time.