Paradigm Ref Studio 80's - Minimum Tube Power?

I am looking at going to a tube amplifier (or tube monoblocks) to power a set of Paradigm Reference Studio 80's. Specs on the speakers say that suitable amp power range is 15-250W. What would be a "good" minimum power rating for a tube amp to appropriately drive these speakers? More speaker specs:

Design: 3-driver, 2 1/2-way bass reflex
Crossover: 3rd order electro/acoustic at 1.8kHz - 2nd order electro-acoustic at 400Hz
High-Frequency Driver: one 25mm PAL pure-aluminum dome, ferro-fluid cooled
Bass/Midrange Driver: one 215mm MLP mica-polymer cone, AVS diecast heatsink chassis
Bass Driver(s): one 215mm filled polypropylene cones, AVS diecast heatsink chassis
Performance:
Low Frequency Extension: 27Hz(DIN)
Frequency Response:
On Axis 0 degrees: +/-2dB from 40Hz-22kHz
Off Axis 30 degrees: +/-2dB from 40Hz-20kHz
Sensitivity-Room/Anechoic: 92dB/89dB
Suitable Amplifier Power Range: 15-250 watts
Maximum Input Power: 180 watts
Impedance: 6 ohms