Tomo P - as requested. The SOP for 8th AF was for B-17s to fly separately and higher than B-24s and for escort to generally fly 4-6,000 feet above the boxes of bombers they escorted.
The B-24s were faster but they did not perform well above 22,000 feet while the B-17s best performance for heavy load cruise speed was at 25,000 to 26,000 feet.
The cruise speeds were 150 IAS for the B-17 and 165 IAS for the B-24 which, at their standard operating altitudes, were about 205 and 215mph respectively.
The cruise speeds for escorting Bombers at 25,000 feet. The high cover for the Mustangs were typically 225 IAS at 28K feet and 200+ IAS for the P-47s at 30,000. This translated to 290-310 TAS, requiring escorts assigned to one box or set of boxes to ESS above the formation in order to not outrun them.
The higher altitude philosophy for 8th FC was about a.) intercepting German fighters as far away from the bombers, and b.) being able to go downhill after German fighters attacking the bombers at their own altitude. Occasionally US escorts were bounced from above in this scenario but I have reviewed many encounter reports in which the LW was intercepted at 27-29,000 feet for 190s and higher for 109s if the P-51 or P-47s spotted them in high cover positions in time to climb and meet them in time.
Usually the fights went immediately to bomber altitudes, then frequently to middle altitudes and then all the way to the deck.
To add to the distress to the LW is that FTH for the first couple of hundred Mustang B (P-51B-1NA's) was 29,000 feet where it would run rings around the Bf 109G-6 and Fw 190A-7..