Well, after owning and playing this guitar for a while I'm really happy with it. Coming up in the '60's these guitars and Gibson ES's were considered by most musicians as "old man" guitars. So, I've spent a lot of years on a self imposed hiatus from owning them. After picking up a couple killer old Gibson ES guitars some years ago this style has become my favorite. Sound wise this guitar sounds every bit as good as the Gibsons. Which surprised me because of it's tailpiece. I've always preferred a stop. When I bought this I fully intended on converting it to a stop but after playing it I decided that would be silly. Playing wise it's really good until I get up around the 17 fret and higher. The notes there sort of choke out a bit and it's hard to get them to sustain. My Gibsons are fine there. I'm guessing that may be the floating bridge kicking in but I can live with it. With some gain the guitar has such a rich, full tone I was amazed when first cranking it up. Anyway, old dog, new tick, killer guitar!!
The Guild/Gibson comparison is inevitable, given the obvious similarities (in appearance at least) between some of the most popular electric models (S100 Vs SG, Bluesbird Vs Les Paul, X-175 Vs ES-275, & SF-IV Vs ES-335)
As far as I'm concerned, and as player of each of these, I will say that with the exception of the Bluesbird/Les Paul duel, Guild has been winning end of the contest.
I have found that playability of vintage Guild at the highest part of the neck, as you get closer to the body and beyond, is often a bit less comfy than it is on Gibson's, but the tone has allowed me to overlook this minor detail in most cases, and I believe. as you mention that it is a tailpiece issue, that has actually been addressed/remedied on the S-100, when the gap between tailpiece and bridge was adjusted.
Unfortunately I do not own one of these "adjusted" guitars, but be that as it may, the magic of the HB1's, combined with the neck ergonomics, has always made the S-100 a big time winner over the SG in my house.
The x-175 Vs ES-275 is probably where it gets as close to a tie to me, but again, the HB1's work their magic on that jazz box , and the fact that one can own a (vintage) Guild X-175 for a fraction of the cost of a Gibby, makes it a no brainer.
As far as my exception (B-Bird/Les Paul) note that I am comparing models from the modern era, as I have not owned a vintage Bluesbird, or a vintage Les Paul (in this price range I prefer buying a house, sorry) to compare both.
But on the ones I've owned, neck profile and pick up's punch have decisively tipped the balance in favor of the Les Paul. (I will now retire to my quarters where I shall endure my penance)
Glad to hear you enjoy the 66!