Obviously, if the front EFX speakers can match the mains, that would be optimal. That said, I used a set-up similar to yours for many years, a smaller version of my mains for the front EFX speakers. Worked great, because the voicing matched.
I'm currently using non-matching speakers, but with some EQ applied to better match the mains. I'm happy with the way things sound, although it did require a bit more effort to get them to blend well.
Regards,
Wayne A. Pflughaupt