Want to know who's right? How about Prometheus?
http://www.laylax.com/list/eghardgear/index.html
Run it through a translator:
http://www.babelfish.altavista.com
In case you can't figure it out, it says that both the genuine torque and high speed torque gear sets can handle up to MS110SP springs.
If you're intent on using the KM 120M, that should be okay. It actually settles to a lower FPS. I installed that spring on my AK and it shot 390fps at first, but has now settled to 380fps. It's also a "relatively" softer spring than SystemA or Prometheus, so is easier on your gears to crank it.