So, turns out this actually went to plan quite well.
The 'Large' size based on 2014 geometry, with a 40mm stem, 780mm DH bar, and dropper post actually fits my 5'7" wife brilliantly. Slam the seat forward to get a steep effective STA, short stem brings the bars back to brilliant, and the geometry is actually great for a long-legged all-mountain bike.
This made me feel good about moving to the XXL size myself (50mm stem, 810mm bars).
I did get two seasons of riding out of that bike, one of them in this configuration. I did like the extra travel and plushness in the chundery and big (well, less small) hit trails I enjoy - everywhere else the BB height increase made it feel less dialed in for handling. The Ride9 full-slack setting made this usable, but not being 'in' the bike at the right settings did make it feel like a slight drawback, especially with how capable the front end can be on a 160mm fork 29er.
Fast forward to converting that into the wife bike - I found that I can run it closer to 50% sag (yeah, that's some Damien Oton level silliness), and put the BB right where it actually belongs. Handling comes right back, and the stock spacer configuration actually means the travel is usable. What was previously slightly excessive LSC/HSC response, with less air spring pressure (relative to rider weight) actually turns into a well-damped system with great control on small and medium-sized hits. What it gives up are the big hits (i.e. it can bottom now, and does not do so as gracefully), but in that application she isn't bottoming it, but instead having piles of traction everywhere.
I found this article actually quite informative -
https://nsmb.com/articles/steve-mathews-suspension-guru/
Only practical downside here is that the pedaling performance (effective anti-squat) on the leverage curve for the bike is a bit off, meaning the suspension is neutral in all but the lowest few pedaling gears. Great for traction, but the efficiency loss is noticeable, especially putting a <150lb rider on a >30lb bike. It really does feel backwards, having me weigh 100lb more and on the 29# version of the bike, but it is what it is.
I have tried to make up that difference with a MinionSS out back - great desert tire for efficiency while pedaling, and the massive amounts of plushness and negative travel actually cover up its lack of knobbiness great in the dry - and on wet roots/rocks the laws of physics come back with a vengeance, but living in the desert that's a trade I'll make every day, especially for a bike she seldom rides in the wet.
The other version I had been contemplating was getting a Metric Trunnion 55mm travel shock (I think it's the 185x55 size), custom bushing connection, and rocking that. Would make it a solid 140mm travel bike, and the only immediate drawback is bushing performance in initial stroke, but that's less of a sever problem. If I ever decide I 'need' more performance out of my current setup, that's a direction I'd look at.
The alternative would be moving to an Avalanche coil shock - a bit pricy even for the basic/simplest one, but they do have drop-in sizes that are long-shock, and if you're looking to really pick up performance, I think that's actually the direction to go, unless you want something mildly exotic, or find a deal on that oddball trunnion size.
On my setup (XXL, Pike150mm 46mm offset w/ Vorsrprung Luftkappe), the shock is a DVO Topaz in the nominally correct size (technically 50mm travel, making it a 152/127mm bike, or 6"/5" travel setup).
This shock is impressive on damping performance, and tunability, even at my limited level of experience on this. The external reservoir and bladder-driven compression adjustment range works great out of the box, and plushness matches my sillier >45% sag setup on the long-shocked Monarch. The rampup is a bit aggressive stock, but for my clyde size it's actually quite a practical trade.
To me the limitation remains pedaling support, but that's more of a result of me going to a 30T oval ring (and eTRS 9-46t cassette) losing some of the kinematic anti-squat, then trying to bodge that with the LSC platform, but I have a really wide sweet spot if I want extreme ground-hugging performance at speed.
Grip performance, even with low-grip rear tires, is enough that I'm PR'ing downhill trails out of the box, and knocking on KOMs for trails that suit me... There's a lot of other variables at play here (carbon wheels/frame/crankset, fresh tires, better sizing and cockpit fitment, freshly rebuilt fork, fresher drivetrain), but the part of that I'm personally able to attribute to shock performance also says there's a real improvement on a piggyback shock with that much adjustability.
As far as pictures, unless you know it's a long-shock setup, most people don't realize it is. Even studying the BB drop closely, it sits right where most 650B bikes are relative to the axle-axle line static, and running more sag it just looks right.
I'll dig for pictures, but they exist on here already.