Sonus Faber vs Wilson

With respects to how long you’ve had your SF speakers, i can for sure say that IF you get those Wilsons, you will sooner or later have next itch, what happens with a separate power amp. No matter how nice you think the Gryphon is, a separate power/ pre will get you to next step. I have been in this situation myself. It just never ends. Also, a system is so room dependant so there is no way you can compare those speakers without swapping them back and forth in same environment. Have you ever visited a true state of the art room acoustic center? I say you will be utterly amazed when you realize what room acoustics do.
What kills most of the overall sound is room nodes (bass peaks and dips).
These are also not solved with the typical room acoustic devices (bass nodes).
If you measure, you’ll have the facts clear. So again, consider listening in your room and also consider if you possibly will ask for a new power/pre amp in a few years.

I personally quit all hifi for years and years because i got OCD. Nothing mattered but the system and it’s updates. 10 years later i still pay for stuff i don’t own (sold it all).
To reroute back to you, who you are will determine how you behave with this hobby. 18K is alot just to change speakers in less than ½ year.

OP, Having a Gryphon amp and SF Strads at home, I can see why your considering Wilsons upfront and less dark sound, but I have a suggestion. 
Go listen to Gryphon Pantheons. I heard them last week with Essence stereo amp and was frankly blown away by the better mids and clearer highs and same bass. 

I also know your dealer.  And those speakers.  They are an easy load so your amplifier will love them.  Getting back to John Ic... if he sets the Sasha's up for you, which of course he will, you will be forever glad you made the change.  As long as your bride is in for the trip.  As to his listening space, it's fine but small, a larger, better designed room would sound even better.  Suggest you take your wife over, have lunch, meet John and let her make the final decision after seeing and hearing the Sashas.  Happy hunting.

All I can say is you must be filthy rich.

My wife would kick me out of the house if I purchased a pair Wilson's.

I like Wilsons a lot but 2 things mentioned in a few answers.
1. Wilsons are not an easy load. The newer ones are better but they still drop to 2 ohms or lower at spots and are very reactive. But good amps designed for these characteristics will work very well.
2. Wilsons like big rooms. But they can be set up to be excellent in small rooms. I've heard Michael Fremer's Wilson XVX speakers, much bigger than the Sasha and they were excellent in a small room, so small that almost everyone would look at it and foolishly not even try the speakers there.