S8955SS 2K with big block top case and larger gears.
Reinforced and redesigned top case and gears make the servo more than durable than ever.  New design helps prevent wiggling pins inside the top case which could create gear gap during flight and could be a cause of damage to 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
Recommended for giant scale ailerons .Jet- Good response on 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.