Mileage adjustment for 996 Cab/coupes

[ian_cab28]

What is fair value adjustment for an above average mile car bought privately/retail. Looking at 2002 post facelift cab/coupes, the retail average is say 35-40k, what would be a fair reduction for say the same car with 75k on it, I'm thinking c.£800 per 10k and would say the £2.4k reduction compensate for the fact that the car would be knocking on or past six figures come resale. I'd plan to run the car under a porsche warranty and would be hoping to see a new engine by this point?! Ian