So you're going Europe-Africa-Russia-US? That looks like a lot of backtracking. If you can visit your destinations in no particular order, you could fly to SVO earlier on your trip (OK from PRG, for instance) to save a bit on MPM. Or wait till SU joins ST and fly direct from CAI
Or you could do JNB-CDG-LED (take the night train from StPete to Moscow and back) and LED-CDG-BWI
BTW, in some RTW programmes you can buy extra MPM in increments of 100, I believe, which makes sense in your case