Looking at Floorstanding speakers, I notice some brands have a dedicated L + R speaker, making me suspect that they would not perform well if I took one and used it as a center channel.
Are you asking about speakers that have some drivers, especially tweeters, mounted slightly off-center? If so, you are imagining a problem that doesn't exist. You can use speakers with off-center tweeters placed on either side or in the center, it doesn't matter.
High frequency sound coming from tweeters will interact with cabinet edges, causing small peaks and valleys in the frequency range of about 4 to 8 kHz. The exact frequency is determined by the distance from the tweeter to the cabinet edge.
If the tweeter is centered in a cabinet, there will be two tweeter-to-edge distances that are the same, creating the possibility of larger peaks and valleys. If the tweeter is slightly off center there will be two slightly different tweeter-to-edge distances. They may generate more peaks and valleys, but they will be smaller in amplitude. That way the speaker's frequency response curve will be smoother.
Off-set tweeters and rounded over the cabinet edges on a speaker have the same aim, to minimize diffraction peaks. They are nice touches in a cabinet, but they make small differences in the
measurable sound. Note that I say it can be measured, but it is not known just how audible a difference it makes.
Does anybody have recommendations on good quality speakers that would perform well as a L,C,R setup? Because budget isn't set yet, I'd like to see recommendations in two categories:
<$10K for all three speakers combined (~$3K Each (or less of course)
<$20K for all three speakers combined (~$6-7K Each (or less of course)
In these price ranges, you should listen to everything you can, and do not settle for the first thing you hear.
I recommend the Salk HT2-TL floor stander. Jim Salk would be glad to build a center tower where the tweeter is centered, if an off-set tweeter offends your sense of symmetry

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