Follow up: usually a small and bought a medium. While they looked passable, there were definitely areas that were baggy—mainly in the thighs and knees. Measured against a size small P10-S, the calf portion down to the leg opening are the same, so I didn't want that to shrink. Soaked it in hot water in the tub while keeping the non-shrinking target propped up against the side to stay dry. Decided to gamble with my thousand-dollar pants and tossed them into the dryer on the hottest setting.
Results: the waist area shrunk down to about a quarter inch shorter than the P10-S smalls. Laying them on top of my other pair, the rest of the pants are virtually a size small now. I'd still buy my regular size when available, but I turned a risky impulse buy into a perfect situation for myself.