It depends!
The 1:10 ratio is a starting point to minimize current draw, but with a 200 Ohm source impedance I'm not sure how much of an audible difference you'll hear - all other things being equal of course<G>!
Try 200 ohms (half power), 600 ohms (which will load the microphone) and 2K Ohms - see which you like better for a given source.
One word of caution - some microphone preamplifiers that claim to change their input impedance don't really do so. This has become one of those points of argument that can generate very long threads at other forums<G>! Anyway, sometimes they simply change the series R, sometimes they change transformer taps, etc. Each of these approaches has benefits and disadvantages (such as changing the gain)...
The real question ought to be... "If you like the result do you care?"