Late to the party, but there is a unique and rare Cary Audio 300b amp that outputs 20wpc using KR300b XLS. 300b SEI LX-20. It has higher fixed bias, more powerful output transformers and circuit that puts 550V on the grid. Downside is the KR tubes are $1,300/pr. I also have a Willsenton R800i 845, with 300b driving 845 output tube to 23 wpc.
I can’t get either amp to one-half on the volume pot with 99dB sensitive Klipsch Fortes. They also drive my Focal Aria quite well at 91 dB. The Cary has a taller, deeper soundstage, but not by much. The mids and treble are about the same, the Willsenton has a touch more bass, but both have SET sweetness. The Cary is a zero feedback design, the Willsenton is a feedback design, but the Cary distorts less at higher volume du to stability of the KR tubes.
If I had to pick one, I’d pick the Cary. I’m fortunate enough to keep both, each in a different room with different rigs.