I think for the size of the head and arm, the whole body and legs seem a little small and out of proportion. I also agree that the legs don't feel dynamic enough. With my dreadnought i had to cut the leg into lots of different sections and green stuff back the details but it came out a little more poseable than the one they supply you with,
and yet it seems rather static, so if you really want a leaping feel you have to almost make a base where there is a rocky outcrop and he is jumping from it?
I think what might be needed is a bit of kit bashing, for example using a pair of defiler claws or legs perhaps as replacements to the standard dreadnought legs, this would also offer a greater ease of a dynamic pose and conversion work.