Good to see you back here, Garry.
I'm slightly confused.
At 25.5", I've taken D'Addario .007s up to A4 on a cheap Samick. They typically snap in unusual places after a couple days. Garry's strings last much longer than stock D'Addarios, but they do feel a little different.
One comment for everyone here to contemplate - Are you familiar with pedal steel guitar? These instruments have a scale length of typically 25-26", and the highest string is tuned G#4, with a pedal that takes it up to A4. This is the same scale length as the guitars we speak of, with a string tuned a half step lower with a semitone bend available. This is in standard E9 tuning, so it's nothing special for country players to deal with. Why does it seem like brain surgery to try to replicate this tension in rock music?
Some of the older classical players, by the way, had seven string classical guitars with a high a.
I have my Oni strung with a 23 5/8" high A4 for years now, and I've had no more string breakage problems with the high string than I've had with any other string. I've never had much trouble tuning my crappy Samick or my $79 Dean with a G#4 at 25.5" with plain old D'Addarios.
I just can't believe that it's this much trouble for the members here.
Maybe it's the bridge, or other hardware - or maybe it's the more aggressive playing style.
I would urge you all to keep experimenting if you want to tune up. I know some members here had a rough time with the O4+ strings, but I'm pretty sure there was some extenuating circumstance, because I've never had mechanical issues with mine. I'm pretty sure if I can take a poorly made Samick seven string and tune up to A4 with an ordinary .007, a little sandpaper, a toothbrush, and a couple hours patience, that you guys should be able to figure this one out.
Incidentally, have any of you tried the RPS strings made to withstand higher tensions?