$3500 floor standing speakers used. What would be your choice ?

Revel plus one ... you cannot go wrong

The sky is the limit and there are so many used speakers to choose from it would be hard to listen to them all. I like Vandersteen and Ohm. For rock and your tube amp, the Tektons would certainly match well. A used or new Salk would be on my list too. Magnepan may be too hard on your tube amp, I know they were on mine. Perhaps look at Emminent Technology?

Just a question, how would used Vienna Acoustics fit in this conversation? 

@2psyop   Salk has been out of business since 9/15/23. Eminent Technology manufactures only 2 loudspeakers LFT-16A and LFT-8B, and both are very inefficient not an ideal match for a 60 watt tube amp. A used JBL 4349 would be a much better speaker over any Tekton model for those about to rock!

I would listen to Vandersteen and Monitor Audio.  Different sounding, but both leaders in floor standing speakers that are not stratospherically priced.