if you don't have to worry about more people than, say, you and a significant other watching television, i would suggest you try going without a center channel and just sitting in the sweet spot when you can.
people like them for off-axis listening, of course, but i've never liked center channel speakers when i could sit within a couple of feet of the center.
that being said, if you do need one, i agree that it should be as close to full range as you can get. i've heard systems where the center speaker wasn't in the same frequency response league as the L+R speakers and it sounded bad to me. and i would think that even 80 wouldn't be a great low end. i had a center that went to 50 and it didn't seem to be enough to me. tons (too much, if you ask me) of sound is sent to the center channel normally and you'll miss it.
people like them for off-axis listening, of course, but i've never liked center channel speakers when i could sit within a couple of feet of the center.
that being said, if you do need one, i agree that it should be as close to full range as you can get. i've heard systems where the center speaker wasn't in the same frequency response league as the L+R speakers and it sounded bad to me. and i would think that even 80 wouldn't be a great low end. i had a center that went to 50 and it didn't seem to be enough to me. tons (too much, if you ask me) of sound is sent to the center channel normally and you'll miss it.