Not having been in this situation and really IG would be best person to reply as he has done folk for speeding in the course of his career to date.
But..
you say he was pushing the old envelope so he cannot dispute he was not speeding at the time.
His lawyers say they want all the facts. They are looking for flaw in application of the law... the so-called "Loophole" where a mistake in the procedure of clocking his speed can undermine their case badly. Example - when the device was calibrated and checked - that sort of thing. That's why I think they want to see this so that they can argue the case to mitigate (per legal beagle in family)
In the meantime .. think back. How long was partner "hooning it along a bit" for? When did he notice the police car clocking him? All of this .. plus any mitigating circumstances concerning livelihood .. all of these factors should be argued out for his benefit by his brief whether he pleads guilty as charged or enters a N/G to get hold of the evidence against on basis he can always plead "Guilty" when he's seen the evidence and in the dock.