FWIW, I've got some charts for the JT4A (707, DC8) and the PW 4056 (747-400 etc.).
The JT4A at 30,000 ft shows a marked increase in maximum continuous thrust from about 5100 lb at 250 KTAS through to more than 5700 lb at 550 KTAS. Wow those TSFC numbers look ugly. Did they give Jet A1 away?
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.