Mach is measured by airspeed, not groundspeed, so whether the plane had caught a favorable jetstream or not is entirely irrelavant.
The SP, with much less weight and the same wing as the 747-200 and -300, could fly significantly higher and faster - the limiting factor (depending on the latitudes) was that flying as high as it could (49,000 feet was not unheard of) led to fuel icing problems, as the temperature of the fuel in the tanks dropped below -30 degrees (or is it -40) which is the freezing temperature of Jet A fuel. Normally, exterior temperature is colder than that, -50 or -60 or so, but friction of the air over the wing will warm it up slightly, bringing the fuel temperature back to operating levels.
I read an article written by a former PanAm SP pilot who described such flights quite nicely - I'll try to find the link.
Flying higher also allows you to fly faster, as there is less drag resistance.
The new Polar flights (like JFK-Hong Kong) apparently also have this fuel freezing issue to look out for, and requires extra attention during the flight over the cold polar regions.
The only thing you should feel when shooting a terrorist: Recoil.