I would buy at least one 28mm figure to go with my average joe 1/72 figures and that would be a correctly done character figure of Harald Hardrada(at least according to the Saga)in Emma... and thats being conservative..
A few Figures(pun intended)
BEF would have to be 23.6mm minimum to be accurate for 1914(5ft 7inches tall otherwise you get sent away)
Roman Soldiers official height is 6 Roman feet(5ft 10inches) so 24.7mm in 1/72... but shorter(and taller) men were accepted... largest foot size I know off is size 14uk 15us for a roman military boot.... belonging to a Centurion
I have not bothered to read the expansive list of responses to this post. However, that said, I have always enjoyed the discrepancies of size believing they add a touch more realism to the craft. Many is the change of command and retirement ceremony, I participated in, where troops lined up from tallest to smallest behind the squad leaders to form the platoon. People are different sizes and piecing these slightly different scales together merely reflects that.
To quote from BLACK ADDER GOES FORTH, "King and Country would have us believe that all British soldiers are strapping 6 footers with muscles the size of Bormoth." (my apologies to those across the pond if misspelled) And the Germans never obtained divisions of their 6 foot, blond haired, blue eyed, ideal soldiers.