Well armor and penetration values are always difficult. From reading around then Sprut-SD has equal protection to a BMP(23mm AP protection)
M1A2 should have larger damage than Sprut-SD. Because the newer M829A2/3 rounds have longer and heavier penetrating rods compared to Russian 125 rounds. The autoloader in Russians legacy tanks limits how long and thus how heavy they can be. This means that despite the larger gun caliber of Russian guns there is less energy going down range. According to all the info I have seen the 3BM42 projectile which you use is roughly 2/3 the damage of M829A2 and roughly half of the A3.
The M1A2 SEP values seems to be in line with Common Armor value system. Using those values your round should do 490 in damage.
Oh I thought that thing in front of the hatch was a rotating periscope, thats what it seems like when you use the tank in game.