Well, here's something interesting! (Or not, but
I found it interesting...)
I just went and played the high frets on most of my PRSi. Main observations:
- On my 2002 CU24 and 2014 P24, both 24 frets (duh), I feel very comfortable playing all the way up to the position where my fingers start at fret 21 and cover up to 24 easily, with my thumb still wrapped around near the bass strings (what the heck is that called? 21st Fret home position or something? I'll use that term, feel free to correct and I will update...)
- My SE-7 (24 fret) feels similar to the CU24, but the wider neck does make it a bit awkward at the 21st fret home position, and it is actually a little easier to use the 19th fret home position and just let my pinky and ring finger make the extra reach as required.
- On my SE Akerfeldt, which also has 24 frets, the 17th or 18th fret home position is "normal", but when I reach about the 19 fret home position I subconsciously move my thumb to the full back of the neck or even around near the treble strings because it hits the neck heel, but still feel comfortable playing up to the 24th fret - but it definitely feels different than my CU24 - never notice until this experiment.
- On my SAS (22 fret) it is almost worse - I am OK up to the 15th and 16th fret position, but I am tempted to move my thumb when I hit the 17th fret home position - the neck heel on the SAS is much bigger than any other PRSi I own.
- On my HB (22 fret) the feel is similar to the SE Alkerfeldt - by the 19th fret home position I am moving my thumb
- On my Les Paul (22 fret), I do pretty well the same as the SAS, might even be worse - by the time I hit the 15th fret home position I am really tempted to move my thumb, and it has shifted at the 16th fret home position.
- My mexi-strat (21 frets) is much more like the Akerfeldt or HB: at the 19th fret home position I shift my thumb.
And to be honest, I find it a bit uncomfortable reaching for the bass strings when so high up the neck regardless of guitar. But! Also to be honest, once I'm moved my thumb, reaching those bass strings is easier...so it is slightly easier on the non-CU24 shaped guitars, oddly enough.
In summary..although the SC shape affects how I position my hand, the other double-cut guitars aren't all that much better. The CU24-based shapes are by far the easiest to maintain the normal wrap-around thumb grip all the way up. Oh, and because I have relatively small hands, although my thumb wraps around the neck a bit, I can't actually fret the bass E-string with my thumb while still fretting the other strings with the rest of my fingers like most guitarists. So perhaps my observations will be very different from others for that reason alone...
I am now intrigued by the very early CU24s with very small heels...