Just my 2 cents.
I believe the ideal is to have 3 identical speakers across the front. But, like you, for most of us that is an impractical solution due to room and setup limitations. That is precisely why speaker manufacturers design and produce horizontal center channel speakers. When they design these centers, they do their level best to voice them so they fit as seamlessly as possible with the rest of their speaker line.
If one can easily use an identical speaker as a center channel, by all means do so. If that is impossible or even inconvenient, I don't believe one is sacrificing all that much by using a well designed horizontal center from the same folks that designed the L & R fronts. YMMV.
