Shai, where are you getting your letter frequency from?
I think that the positions of Z, X, C, and V are actually rather difficult to type as command keys. The index finger has to stretch down to be near the thumb. I think the easiest keys to type while holding cmd/ctrl with the thumb are (QWERTY positions) A, S, Q, W, and E. If you move to the right more it requires a bending of the wrist. For the sake of commands, the best thing (for a mac) IMO would be Q in Qwerty position due to being next to tab (command-tab + command-Q to quit), the H being next to Q (command-tab + command-H to hide), C being in the R position (which is a little harder, but still easier than command-V), and Z, X, and V being in the same place because I don't use them as much, they can't go on the home row, and there's no other good place for them.