Sensitivity 86 v 90

Another thread with a lof of misinformation in it. I especially like the misinormation with exclamation points.

I would be concerned. Tube amps don't usually double in power from 8 to 4 ohms so moving to 8 ohm speakers will probably give you even less total power to work with. Especially if you're already almost max'ed out.

Tube amps usually put out the same power into 4 or 8 ohms so that might not make any difference.  But I am surprised that your tube amp has to work so hard to drive your 90db sensitivity speakers.  I have a much lower-powered tube amp driving Vandersteens (sensitivity 86 db) in a moderately large space to volumes higher than I want to listen to.  Perhaps the input level to your amp is too low?

If the ratings are reasonably accurate (a BIG “if”), the 8 ohm load of the lower efficiency speaker might make it a better match than the higher efficiency speaker.  I generally find that an easy load is more important when it comes to tube amps.

 Not knowing the size of your room, how loud you listen to music, etc., it is hard to speculate on whether you have enough power.  I generally expect 80 watts with 86 db/w speakers would be sufficient; at least I would not rule the amp out.

Look at the impedance dip. That is where things make a difference.

I had Salk Songtowers...easy to drive at 6 ohms and 88db efficiency with 30 watts. And great sounding speakers in their cost range. BUT it dipped into the 3 ohm range momentarily. There are subtle things that come to the fore with 93db speakers that I didn't so much with 88db.