Will you accept first hand accounts? Or just pure data? I can give you a perfect example of why the 57 earth pet is better.
https://wiki.project1999.com/A_frost_giant_elite
The elite's in greater divide have around 6500 HP and are level 45~ or so. The 49 earth pet will die halfway through that fight and you'll need to summon another one to finish, and you would have to DS it again.
49 earth x2 + DS x2 + Burnout = 200x2 + 155x2 + 150 = 860 mana
57 earth + DS + Burnout = 400 + 155 + 150 = 705 mana
Then you would have the factor in the lost med time, when you would be re-summoning the pet, rebuffing the pet, running around like a chicken until the pet gets aggro.
I know this first hand because I would exp on those guys at 56 using Dyzil's (level 41-45) which is even higher level then the 49 earth(37-41), and would always need two pets to finish the mob. Once I got 57 and swapped to earth, it finished the mob by itself 9 out 10 times, and than I would just have to tank a little bit at the end, that's when the summon is the lowest level.
Now I'm not saying the shoveled 49 earth isn't worth using past 49, because it is, and there are plenty of exp spots where it's viable. If you don't have a water or air staff, it's prolly the best pet to use until 56 when you Dyzils, and then 57 when you get the final earth. If you really need logs I'm sure I can dig some out, but it's completely unnecessary, anyone can tell you that the 49 earth has a shelf life.