[MetalMan]

The motor can only put out as much as the batteries put in. The ESC does affect performance slightly, the more amps it can handle, the less resistance it has which gives more power to the motor. But, the batteries are the limiting factor. If an ESC can't handle a motor, then it will get hot and possibly smoke. You could possibly use a lower-current rated ESC, and set the acceleration to slow, but then your acceleration would be slow.

The amp ratings on ESCs don't really affect speed, except in the very minor loss that they have due to their resistance (more amps they can handle, the lower the loss). The MGM 120amp should (theoretically) be able to handle more than the Quark 80amp, simply because it is rated higher.

You're not going to have much luck finding a 6s Lipo controller under $200 that will be able to handle much besides the 9920 or Quark 80amp (that can handle a decent amount of current). But, if you use a higher battery count (like 6s Lipo), then you could possibly use a controller that is rated to use fewer amps. With higher voltage and a slower motor, the current draw will be reduced (assuming the gearing is appropriate).