S8955SS 2K with big block top case and bigger gears.
Reinforced and redesigned top case and gears to make the servo more than durable ever.  New design helps prevent wiggling pins inside the top case which would create gear gap during flight and could be a cause to damage the gears.
 
Stall torque:   34.2 (6.6V) / 38.3 (7.4V) / 43.5 (8.4V) kg · cm
                          474.7 (6.6V) / 532.2 (7.4V) / 604.1 (8.4V) oz
Speed : 0.06 (6.6V) /0.06 (7.4V) /0.05 (8.4V) Sec / 60 °
Weight: 85.5 g / 3.02 ozLead length : 300mm
Operating voltage: 4.5V – 8.5V
Operating angle: 120 ° / 150° / 180 °
Programmable
Recommend for giant scale ailerons .Jet- Good response to jets.
 
The firmware in a 2k servo verifies the position of the servo arm two thousand times each second, 
while the firmware found in previous servos verify the arm's position one thousand times per second.
This greater number of verifications makes for a very precise servo, and gives it a more "solid" feel.
It is recommended to use a booster cable with 2k servos to ensure steady voltage at all times.