Is it the low mileage blue one by any chance?
I've yet to see many, if any GSR reach that price tag. So I guess it's hard for any insurance let alone a specialist like Paceward to justify such a premium when market values at best are -£5000 from your estimated valuation.
If this was the case everyone would be insuring the cars at £100,000 and then going missing every week.
Have you any documented history, indication you can show Paceward that gives them an indication why your example would be worth a lot more than others for sale? This may help you.