Raven Blackhawk LE... am I going to be disappointed?

88dB is pretty low. 92 is my cutoff for consideration, and you are well below that. Still, what really matters is you prefer quality over quantity. The Ravens 20 tube watts is comparable to 50 to 100 solid state pseudo-watts, and you already know you prefer a really nice sounding 75 to not so nice 225.  

There's people in your situation who have been disappointed, but they never write detailed reviews so you never really know, it may have been all down to unrealistic expectations. I think as long as you know you are not buying a high power headbanger and are more into a believable compelling presentation you will probably be find. Captivated, maybe even. We hope!   

Not just saying that because I am in the process of buying a Raven Reflection MkIII either. ;)

I was looking at the Osprey for my Spatial M3 Sapphires 92db and decided against it. Wasn’t crazy about their restocking fee. Although the Ravens seem to be trending now I wasn’t convinced I would be able to push those 15” woofers. I opted for an Octave because I had a dealer close by and haven’t looked back. I wound up with the V70 Class A. The Octave is stunning and can drive virtually anything. You might want to check them out.
https://www.octave.de/en/index.php

room size and how close you listen are important factors.  
i had the raven blackhawk driving KEF LS50s in a medium large room that everyone said would not work.  fortunately you listen with your ears and not on paper.  the sound was spectacular.  
you are in for a treat.... 

Cool.  Thats kind of what I was thinking.  I’ve only ever had one tube amp, a prima luna prologue 3 or 5... cant remember.  I like it but Im thinking that the Raven will be a step up.  
I may roll tubes and if I like the Raven but it doesn’t get loud enough, I’ll switch speakers to something higher efficiency. Choices seem limited though to ZU, Spatial and Tekton...