Yep. This was going to be the next phase: there isn't anything special about the SI system, but it is consistent. The poster didn't seem prepared for "or any other velocity units you want".

For the original poster, you could equally use c in miles per hour, mass in "pounds", and get whatever that produces for energy (I'm sure there's a name for it).

This is also why Imperial units produce such amusing things as Foot-Pounds (for torque). The math all works out in the end, but you get some amusing numbers along the way.