Will,

I tend to prefer my center xover at 80Hz, along with my surrounds (even though the speakers are a matched set of NHT 2.5, 1.5 and AC-1. The higher xover just clarifies the dialogue a bit more effectively.

I waffle on the surround xover. 60Hz makes for more solid surround effects. 80Hz makes for a bit more "space" around the sound, particularly when using surround synthesis from two-channel source.

I'll never be able to kill the tweaking monkey on my back.