2xhps for flowering would be optimal. You just can't beat the hps spectrum for flower. And then you've got your mh for your veg room.
Cuation is always good, if mainly for your own peace of mind. I doubt the power company would start calling LEOs for that little a power jump. But better safe than sorry has always been my motto.
I think the answer to which lights to use depends on the size/shape of the space. If the space is fairly squared, so that all the plants are relatively under the one HPS you have up now, then I would be inclined to add the MH for full spectrum lighting covering the whole grow. But if the space is oblong, such that the one HPS covers the center but not the edges very well, then I would do the two HPS lights and position them to get good spread coverage over the entire growspace.
If we're talking about adding lights here, I think UVB should be entered into the discussion. Many believe that a UVB light (such as the ones sold in pet stores to be used as reptile lights) increase trich production during flowering and greatly increase the potency of your smoke.
Flouros and CFLs are great for supplemental light, but I see what you are doing trying to manage your electric bill. Good luck to you.