Sender Substitution

I've seen stiff legged calf hops as the suggested substitution, but I was wondering if you could do Jump Rope double unders as a substitution, or are the calf hops better because of the height of the jumps/rebounds?

http://gymnasticbodies.com/forum/viewtopic.php?p=2909#p2909

DU can work but the thing to question is whether the DU has excessive knee bend or not. Question also the rate of frequency of the feet in the DU or the "punching" action in the flexion/extension of the ankles.

Obviously progress in these would be measured with jumping higher. The same is obviously true with depth and box jumps. When it comes to other lower body exercises in the WOD which utilize weight and jumping/speed (ex-killers, 20m backward sled sprint) do I want to add weight , or jump higher/run faster with the same weight? Would it depend on whether the focus of the day is power or strength, or the same answer applies to both?