What is your choice??
Prometheus Double Torque Gear Set + Kanzen 7mm ceramic bearings
total $125
OR
Modify Modular Torque Up Gear Set for 7mm Gearbox (in case it will fit G&P 7mm gearbox)
I also found "Smooth" version
here Which one do you think is better?
Older version seem to be more durable cause have two rails....
total $80
Consider quality, durability and M130 spring...