There is no doubt that the Lightning air data system would be subject to significant errors in these flight regions, but I couldn't state whether they would be positive or negative.
Suffice it to say that when going for broke on one of these profiles you were pretty much in the lap of the gods. Temperature spectrum in the upper atmosphere, good donks, and a good canopy seal. Early models would have been better because they did not have all the fire integrity mods (scoops, venturi drains etc, drag) that the later fleet had. IIRC the service ceiling was 56k as the pressure suit had been withdrawn from service, which meant that depressurisation would result in death above that height.
My personal best was a foolhardy 1.8M at 68k ft. When I cut the burners at my bingo fuel the cockpit pressurisation warning came on, instictively I banged the burners back in to generate some more bleed air and the darn things lit!! But now I was still high and fast, couldn't point towards the coast for fear of the sonic boom complaint, was burning fuel that I didn't have spare, aircraft was at about 150 kts and felt like I was stirring wet porridge when I move the controls. I couldn't cancel the burners again for fear of depressurising myself to death. Ended up in as tight a descending spiral as I could manage to try and slow down. Vowed never to do that again.
Compare that to Typhoon to answer Beagles question then we fall into the trap the nanny state we now live in. The spec calls for a 55k ceiling with "excursions" up to 65k. These have nothing whatsoever to do with the performance of the aircraft, but instead fall out of the dreaded risk analysis which calculates to the nth degree what the chances are of depressurisation and the capabilities of the kit to protect the pilot.
On numerous trials we would zoom at the end of a high speed run and have to perform an aggressive roll inverted and pull to full back stick to avoid busting the relevant altitude limit.
DA2 is coming to the end of its trials life, have often thought what a jolly good idea it would be to strip it down to basics and have a go at some records. Unfortunately neither the funds nor the risk acceptance exists to make this a real prospect.
Sadly such tales of daring do from Messers Carroll/Hale/Roome will not be repeated in this day and age because the "spy in the cab" exceedance monitor will be tripped and the GASO exceed message sent to group before you have a chance to say "sorry chief, jets crook".
Ho hum
Tarnished