Bookworm,
Further remarks from your post -
"By contrast, the PW 4056 is almost perfectly flat at 30,000, while at 35,000 ft there's about 12,000 lb at M 0.5, rising to about 12,500 lb at M = 0.85. It's not much, but it's something."
Actually, it's VERY significant, as opposed to "It's not much, but it's something". In terms of ram RISE, that is, where the static thrust increases beyond it's original value, true, it's not a great deal. In terms of ram RECOVERY it's VERY significant, even if the thrust remained 'flat lined' at 12,000 lb. With increasing speed, the speed differential between the jet efflux and the aircraft forward speed results in an almost linear decrease in thrust, to the point where a jet aircraft could not hope to achieve much more than about M0.6. Even for a 'flat line' situation, the very significant thrust RECOVERY back to normal is due to increasing ram as Mach number increases.
Regards,
Old Smokey