Thanks for the replies, guys.
I think I will have to try and get a test-drive for a few days, to drive one in my normal conditions to see what I get.
My main drive is a 35-mile round trip, about 1.5miles to get on a duel carriageway, 15 on there and another mile or so to the office.
The dual carriageway is 70 all the way, with very little in the way of stop-start, heavy traffic.
That may explain my decent figures up to now.
Thanks again