So, for anyone interested, I actually had a chance to try on the sizes in question in both lengths. We played a game called, “I’ll Try On Pants Without Telling You The Size, and You Tell Me Which Ones Look The Best Or Whether They Make You Want To Vomit.”
The unanimous decision (5 people) was to go down a size. In addition to being short-waisted, I have a 12" difference between my hip and waist measurements and, uh, no thigh gap. They fit almost at my waist (2 fingers below my waist/1 finger below my belly button), but actually fit really nicely when sitting in a saddle (no massive gap in the waistband like I get with Trophy Hunters). I will admit they are slightly snug, but I’ve been working on trying to drop a few pounds and given that I NEVER dry my breeches, I think it’s the right call. (Besides, getting a wedding dress that was too small was great incentive to lose weight before my wedding… so fancy new breeches should work just as well or better, right?)
My personal preference was to go with the longs. They are slightly too long, but still just above my ankle bone, and I prefer the slightly too long to the slightly too short (I really am in-between!). I figure this gives me some leeway if I manage to shrink them (which I somehow did with one pair of TS, even washing on cold and air-drying), but also if I do gain a little weight in the future (one pair of my TS definitely fit longer when I weigh less!). If the length is ever a problem, I could always have them shortened a smidge.
The fabric is pretty forgiving in darker colors, and kind of “supports” things that might otherwise jiggle, hence the sizing down. My regular size, while fine, was just not as flattering (imperfections, from pockets to personal lumps were just more visible). Lighter colors, however - ick! I’ll be sticking with Trophy Hunters for show breeches, and maybe spring for getting them tailored in the waist.
So there you have it - my very scientific assessment of fit. This may or may not be useful to someone in the future, but I decided to share this just in case it might be.