I wonder Pete, if it's as simple as the bridge being the difference (Stoptail -vs- 2 Piece)???
There might be something to that, in the Doublecut. The way the bridge matches up with the dynamics of the Wood in the smaller Doublecut shape, thinner body and different neck/body joint.
To me the Singlecut definitely progressed in tone from the SC 245 Ted to the 2014 McCarty Singlecut Private Stock to the SC 594. I will give Paul and the PRS team a lot of credit in that there is a lot of Black Magic they do to constantly tinker and improve tone. For some reason the experience I had was that I liked my SC 245 Ted's more than the my 3 SC 58's, but then when the McCarty Singlecut came out in 2014, that blew away any previous SC 245. That I believe had a slightly thicker body and no Belly Carve. That had the two piece bridge and still sounded amazing.
I know they did slightly modify that two piece bridge over time, many subtle changes over the years, both in 2016-2017 and again going into 2020. (I had a prototype 2020 that had a slightly different approach than the production 2020's, for the saddle parts.)
So to me my opinion and preference is the Stoptail for the Doublecut and the Two Piece for a Singlecut.
I have commented before many times, what led me down the path of going to the 25 inch McCarty was this great video from Tim Pierce and Howard Leese, as I got excited about the Nitro over CAB finish for the Core guitars, which to me tied back to the Nitro finish of the 2009 Ted McCarty Run and the 3 Willcutt Guitars Wood Library Ted runs.
I thought the SC 594 sounded amazing in the video, but I thought the 25" McCarty sounded just as good! I bought a couple, and that was validated.
In rebuilding my PRS collection here in 2024, I really view my amazing new 25 inch McCarty as an extension of the DC 245 Ted love that I had. To me, it looks like a Ted, plays like a Ted, sounds like a Ted, and emotionally connects me back to my many years of Ted love and worship.
To me these two guitars are the very best of the PRS Guitars available closest to those classic Singlecut tones.
I am still curious to try the 2024 Santana with the 594 scale, and see how that fits into the mix!
Also if I do build a Private Stock later this year, it would probably be a DC 594 or McCarty with a Trem, or an SC 594 with a Trem. I guess I really am back! LOL...