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

I had the Bolero's many years ago... good speakers!   I also like the Proac and Tannoy suggestions.  Just make sure you get speakers efficient enough to pair with 60 WPC tube amp.

Just saw some Tannoy on TMR today.  Real close to your original 3500. Nice cabinet

Open baffles open and relaxed if you have room.  Won't be a problem driving them.

Many speakers take too much power.  

+1 for Totem.   Tremendous value and all around excellent speakers.   Super easy to drive.   Might look at the Bison Towers or similar.

The OP’s description in his second post says ProAc just like his initial post. Just make sure you get enough juice from your tube amp.

Ha… I just spent that this week (but CDN not USD) on a used pair of speakers. Probably not your cup of tea though… Coincident Total Victory but I have desired these for a long time, saw an opportunity and decided I should just indulge. Good Luck with your quest…