Castle Creations ESC recommendations for the HPI Savage XL:

Castle does not offer a motor that will mount in the Savage XL.
The truck uses a clamping mount system that is incompatible with our sensored motors.

The Mamba Monster 2 is an equivalent replacement to the stock ESC.
The Mamba Monster X is a slight improvement to the stock ESC; it adds data logging, aux wire and a bigger BEC.
The Monster X 8s is a significant improvement over the stock ESC. It runs significantly cooler and has smoother low speed startup.