I have included the breed standards for the UK and the US. There are a few other standards around the globe depending upon which country you visit. One of the noticable differences that you will see with the UK standard compared with almost everywere else is the issue of size.
The issue of size is one of the main arguing points between breeders and enthusiasts. Some would argue that the UK standar is more of a range than a standard with regards to this issue, as there is a range of 3 inches in height (Dogs 25-28, Bitches 23-26). The last time there was this sort of range was with the original breed (US) standard which was introduced in 1935, which had Dogs at 22-25 and Bitches at 20-23. The original US standard was changed in 1960, and made the upper limits as the set desirable "freighting size." Although what exact scientific or experiencial method was used to come up with this, is unknown to me. Also I have it on good authority that the UK size was changed due to the fact that there was a lot of big dogs around in those days (1970's). However, I sometimes wonder if it had anything to do with the appearance a few years prior to this change of Mr Brown, and his US standard size Tigara dogs.
There are a lot of good polar exploration books available by people such as Will Steger, Wally Herbert & Rick Atkinson, to name but a few. You will find various references in these works about the efficiency of working dogs with regards to their size.
With regars to ideal frieghting size, there is an interesting piece in the book 'of dogs an men' which is about the British Antarctic survey dogs. In the 1950's a scientist from Cambridge Uni went to Antartica to carry out a series of test on the working sled dogs. Some of the findings were as follows: Opimum size 'sledge dog': Height at shoulders 23" Nose to tail 60" Shoulder width 10" Hip width 8" Weight approx 90lb