Although considerably more efficient than ESLs, the Westminsters are what I would call 'moderately high' efficiency- which means you will need some power to show them off.
20 watts will not do it unless you have a smaller room. I recommend a bit more; 50 watts is a good minimum. OTOH you don't need a huge power amp; with 50-60 watts I imagine you can shake the building and not clip the amps, which is the ideal situation.
The speaker is very tube-friendly so you have a wide range of amps to try. However as pointed out it is also very revealing, stick with a tube preamp too!
20 watts will not do it unless you have a smaller room. I recommend a bit more; 50 watts is a good minimum. OTOH you don't need a huge power amp; with 50-60 watts I imagine you can shake the building and not clip the amps, which is the ideal situation.
The speaker is very tube-friendly so you have a wide range of amps to try. However as pointed out it is also very revealing, stick with a tube preamp too!