Not exact passages from Ops orders, but here are a few quotes from a book "The Mighty Eighth" - all quotes are bomber related unless otherwise mentioned afterwards.
pg 190 - "The Luftwaffe pilots withdrew, bloodied after a series of dogfights at 30,000 feet, prime conditions for the Thunderbolts" - refering to the Schweinfurt raid
pg 229 - "We flew at 24,000 feet going in." - a B17 raid on Frankfurt
pg 255 - "4 March 1944, 28,000 feet over Berlin...minus 65 degrees...[On at least one B17, the bomb doors froze]"
pg 261 - "Our group was near Hanover, Germany, around 23,000 feet and heading east. A gaggle of German fighters were below us around 18 to 19,000 feet, set there as a decoy. Several thousand feet above us was a much larger group" - a P38 pilot on fighter sweep
pg 100 - "We were at 25,000 feet, flew over Bremen our primary target. Engaged by flak and fighters. We took violent evasive action all the while.."
pg 113 - "My last look at our altimeter in the ship was at 26,000 feet" - Navigator Wayne Gotke, after bailing out of a B17
I could find more, but the general theme is that the bombers flew at mid 20's, up to nearly 30,000 even, and the fighters on both sides did the same. This is, for the most part, refering to the bigger bomber raids and not simple fighter sweeps (except the one quote).
When I can find it, there is a passage in one of my books on the RCAF that refers to fighting over the channel, and how both sides felt that fighter sweeps at 26,000 feet were getting out of hand, and brought their sweeps down to about 15,000 feet. Don't go flaming what's in this paragraph as I don't recall the exact words used, just the overall general wording. More to follow.
Cheers