The threads on here have been much use to a newbie owner, so more than happy to contribute, especially if it helps someone sort of justify the cost of running one as a daily (mine has been for about a month but I have a sensible car too!).
Will see what it is this weekend as might take it back down to Cardiff Saturday eve — might take the Northampton/Birmingham route instead for comparison as won’t be overtaken by so many lorries if I go a bit more gently!
Regret to say I didn’t calculate it on the Norfolk to Cardiff run before I got the overdrive installed, but can confirm that I was overtaken on the A14 by a lorry hauling mining equipment
Getting a 1989 with a retrofitted 300TDI refurbed 50k miles ago this weekend. Will provide updates once I’ve done some decent mileage in it!