Walker mounts two chin blaster cannons and two at "ears".
FIREPOWER
I will take starting temperature as -40 ° C. Density of settled snow is approximately 30% of water density, or 300 kg/m^3. So we have 300 kg of snow vaporized.
However, if we take ice instead of snow in equation, then we have 917 kg vaporized.
Data:
-melting point of water: 0 ° C.
-boiling point of water: 100 ° C.
-molar mass: 18.015 g/mol
-specific heat capacity: ~4.2 J / (g x K)
-heat of fusion: 333.55 kJ/kg
-heat of vaporization: 2257 kJ/kg
In order to get high-end estimate, I will take it to be ice vaporized. That way, we have 917 kg of it vaporized.
1) Raise temperature to melting point: 154 056 000 J
2) Melt it: 305 865 350 J
3) Raise temp. to boiling point: 385 140 000 J
4) Vaporize it: 2 069 669 000 J
For total of 2 914 730 350 J or almost 3 GJ. However, "ear" guns seem to be smaller and weaker than these, with my rough estimate (based on differences in size of blasts and presumed volume of ice vaporized) being 17.5 MJ.
RATE OF FIRE
Walkers usually fire 0.5 shots per gun per second (2 shots per second combined). However, one walker in TESB (only appearance of AT-AT to date) fires all 4 guns simultaneously, for rate of fire of 5.5 shots per second (total of 11 shots) or 2 shots per second for "ear" guns or <=1 shot per 2 seconds for chin guns.
Walkers seemed to traverse 1/5th to 1/3rd of their length per second.
From that, we have walkers as being 23 meters tall (OK, Hamill isn't 1.8 meters tall, but boots and helmet should make up for that). Length of walker without barrels is thus 25 meters, and barrels add additional 1.7 meters to length, for total of 26.7 meters, thus giving us speed of 5 to 8.9 meters per second, or 18 to 32 kilometers per hour.
Not quantifable, since we never saw it being fired upon by anything we know or can determine figures for.
However, it seems that AT-AT uses some kind of polarization for added protection against energy weapons, meaning that armor might not be as strong as commonly thought. Anyway, mass can be guessed - modern M1A1 Abrams MBT exterts ground pressure of 15 psi (15 pounds per square inch; or 1.055 kg / cm^2). Since AT-AT commonly has 3 legs on ground, we can guess ground pressure from that.
Diameter of "foot" seems to be 3.78 meters, for total of 11.222 square meters; with 3 legs at ground at any time, it rises to 33.7 square meters, or 337 000 square centimeters; therefore, mass of walker would be somewhere armound 360 000 tons. Given that its body is basically a box, and that AT-AT functions as transport vehicle, it is possible that armor will amount for greater percentage of mass than modern MBT, but lower than modern IFV due to legs and head.
Assuming commander's height of 1.9 meters (due to boots and helmet), and assuming 43 pixels equates 0.9 meters, we get ratio of 2.093 centimeters per pixel, which gives us height of cabin as being 288.84 centimeters, or 2.89 meters.
So we have walker's cabin being 3.54 meters long without guns, and walker itself being ~7.46 meters tall.
On admittedly rough estimate, standard speed of AT-ST (at least in Endor environment) is about half of its cabin's length, or 1.77 meters, per second, which gives us speed of 6.4 kilometers per hour.
We see that shots from AT-ST can blow up wood, but not set it on fire.
Heat capacity of wood is between 1.26 and 2.9 kJ/kg K and density between 110 and 1330 kg/m^3. If we assume that AT-ST can heat 7855 cubic centimeters of wood enough to make water in it vaporize (delta t of ~80 ° C) then we have 0.86 to 10.447 kg of wood heated, for total firepower between 86 688 and 2 423 704 J per shot - that is, between 87 kJ and 2.42 MJ per shot.
Capable of withstanding 4 shots from another AT-ST at same spot. Given above calculations, we can assume that armor of AT-ST can resist to 348 kJ to 9.68 MJ of DE weapons fire at same spot.
