Yea, and although he didn't reveal the numbers; the phrase "flat out scary" MACH numbers coming from a sled driver must mean: really haul'n ass.
//The Mach eases to 3.5 as we crest 80,000 feet//
The Lockheed X-7 topped out at M 4.31, so my guess is M4 tops for the BlackBird fleet on conventional fuels.
When I worked at NASA-JSC a while back, an engineer who had worked on the SR-71 said they really didn’t know how fast it would go. That if you pushed the throttles to the wall it would just keep going faster and faster...until the engines blew up.
The article from the SR-71 pilot seems to confirm that.