The king of long range tank battles is the Jagdpanther. The 10X optics and the 88mm KwK 43 L/71 main gun is truly king in AH. When operated by properly trained crewman or crewmen with a bit of experience it was devastating in WWII. Unmatched, really.
However, the bane of any of the turret-less AFV's in AH is going to be a laddie with the bravado of brass 'nads flying to the flank in an M18.
Don't try and beat the King Tiger, Tiger, Panther, or Jadgpanther in a long range duel using the same long range tit-for-tat tactic unless you have the utmost confidence you can adjust your fire quicker than the other guy. You're only playing roulette when you do so.