There's a youtube video that also uses the eight foot candy cane theory:
It finds out that the adult ponies are exactly 120.24cm tall, or about four feet.
And it also figures out that the strongest ponies can hold about 146kg. Fun fact!
This video shows that Big Mac can lift around 146kg...
It would be neat if someone was able to find out exactly how much a unicorn character and a pegasus character could carry and then compare them.
There a youtube video that finds both the heights of the ponies and the mass of the cake:
http://www.youtube.com/watch?v=3X6p9NuBSgo
For the mass, they find the density of regular cake, find the volume of the cake, and use that to find the mass.
It ends up weighing 146kg.