I'd say for surround use with a modern processor to pick the speaker with the widest, most even , horizontal dispersion(as a bipole). But if you'll always be the only one listening, and sitting in the same sweet spot, then it's probably not as important.
I don't think seamlessly tracking dialogue to the surround channels is as critical. At least, I can't recall a movie or song where I've noticed continuous dialogue moving around like that. Usually the LCR combo is where it's important to match for dialogue (and where so few "large box" systems are truly matched!).
Since you've got dual subs, the lower bass response is just the usual integration issue. *Unless* you're using your system to listen things like SACD's, in which case each speaker is expected to cover the full frequency range at full power.
So you might want to check speaker type, placement, and integration with each type of material (and listening position?), just to make sure your final choices are the best compromises.