I went the opposite direction. I went from a 6SN7 based preamp to a 6922 based preamp. I agree with many of the comments about the 6SN7 and happily rolled tubes in and out on a regular basis. After spending many hundreds of dollars on tubes, I found 2 or 3 pairs that were my favorites, each of which had unique strengths, and enjoyed the ability to change the sound from time to time.
I was a bit apprehensive when I bought my Herron Audio VTSP-360 because I wasn't sure that things could get much better than my previous preamp, but I was immediately struck by how much quieter it was, how much detail it had, and how it presented as good or better of a soundstage and had very precise imaging. Most of what I've read about it indicates that there are not major differences to be had by rolling tubes, and to date I have yet to open the case and am still happily using the stock tubes that came with it.
There's more to the preamp than just the tubes and Keith works magic with his gear. I also own the Herron VTPH-2A phono stage which uses a combination of 12AX7 and 12AT7 tubes. Again, magic happens with the stock tubes.