"HP to be able to go UPHILL" and gain airspeed was great to have. When I was flying F-15s in Alaska we had a favorite route home from STONY MOA that lies to the west of Ptarmigan Pass, approx 100nm west of Anchorage. We call the route "Star Wars Canyon." We start at 500' AGL and around 400KIAS at approx 3800MSL headed East. The route took us through a canyon that got deeper and narrower and much steeper as you continued into it. At the end you were in a 60 degree nose up climb in full afterburner climbing the face of a mountain that topped out just below 10,000MSL. We would continue to climb, until rolling inverted and pulling the nose down to level off, usually around FL290 and still doing over 300-350KIAS. During the climb we would check in with Anchorage center and get our clearance home. We were able to safely and legally do this because we were still in the MOA (SFC-FL500). Tadpole could always tell when we flew that route home because we landed with an extra big smile on our face!
M6RV6. The two time marks you referred to are not indications of Supersonic flight. What you are seeing is the condensation of the moisture present in the air. These form as G's are pulled. The more moisture in the air, the larger the camber of the airfoil the great the effect. The air is accelerated, that acceleration causes pressure to decrease, this causes temperature to drop, therefore a "cloud" forms. No different than watching an airliner with approach flaps/slats set in a moist air mass.
However, as both a go-fast-low and a go-low-slow type of pilot I appreciate the hazards associated with the conflict between these two types of aviation. At least the F-18 and my Eagle had a great radar to help us look for others. I have almost been run over by a B-1 that was on a low-level at 7500MSL out in west Texas. We were both legal. There was no way to avoid crossing the route and Center claimed they couldn't see me on radar. The B-1 passed approx 1500 feet from me, co-altitude from my 7 o'clock position. And yes, the 500' floor is busted on a regular basis at certain locations on each route. Typically around higher terrain points or edges of varying terrain.
Bart: As far as turbulence goes, you are exactly correct. The wing loading pretty much made anything but severe turbulence seem minor. However, the F-15 would produce it's own Mod-Sev turbulence when you were below approx 5,000MSL and going 500KTS plus. Those thick wings and the lifting body nature of the airframe created this turbulence and it was not comfortable or fun!