In most machine shops the rule of thumb is the vise should be mounted so the top of the jaws are between the navel and the bottom of the ribcage. I realize this has limited use for you as you have already decided a good height, but for future reference, or for anyone else looking for a decent height, its a good place to start.
I should mention that this is basically for an all purpose vise. Again, if you are using it as a striking vise, or are intending to work on larger pieces that extend above the top of the jaws, you should mount it lower, but for basic filing, light hammering, tapping, sanding, etc, etc, this seems to be a good height.
