I have a spreadsheet log for my rides where I record avg speed along with a lot of other things about the ride. I very seldom post avg speeds on the forum because of all the B.S. about them on the forum. They are for my own comparison and not much more. If I do happen to use an average speed in a post I make sure to explain that it is a figure from a bike computer rather than miles ridden/elapse time. That way other riders can interpret the figures accordingly.