Wow - thanks for all the replies guys - got way more info than I needed here. Re-reading my original post I can see that I didn't ask my question as clearly as I could have. I already know how to bias one of these (have been working with them for years) and I don't need a mic pre (have been building those for years too), I just always wondered how much voltage would be optimum for this type of mic, which has been answered.
What I need to do is build a biasing circuit that will give me the required voltage no matter what it's plugged into, i.e., if I plug it into a board with an actual 48v phantom power supply, I want it to get, say, 5v (just picking something in the safe operating range here). The same if I plug it into some piece of gear that has less than 48v for its phantom (and there are things that do).
The obvious solution is a voltage regulator, but the max I/O voltage differential is usually 35-40v, so if I do plug into a 48v (or slightly more if things aren't quite in spec), I'll be pushing my luck on the regulator. I suppose another option is to use a zener diode to make sure I get the right voltage... I'm open to other suggestions though if any one has any ideas.