Indeed, Steve, but as you know having heard it, the KT88-based Copper amp I use works even better with some quality high-efficiency speakers on the end than it does with 'normal' speakers...so...
a good push pull kt88 is a good introduction into valves, when used with more 'normal' speakers,
but as marco has come to realise, there are further gains to be had with higher effeciency speakers that match well
its a slippery slope
This proves that when a valve amplifier design is 'right' to start with it doesn't matter what speakers are used - the results are still fantastic!
It brings us neatly back to implementation and how significant it is in the overall scheme of things, because that wouldn't necessarily be the case with 'normal' or 'bog standard' KT88 amps and high efficiency speakers... So one must always remember that the key to success is not focussing on any one aspect of valve amplifier design but: implementation, IMPLEMENTATION, IMPLEMENTATION!
Marco.