Nice project, unless for the tweeter add, there is no practical or musical reason to use such driver hence the Alpair 10P reach 20kHz easily, w/the Alpair you will have the rare feature of a midrange and one tweeter, both OB and Dipole in the same driver with the rich organic tone of a paper cone.
With tweeter you will have:
more parts, more price, more labour
more 2 xover legs to detracte the music
you will have less SPL due the xover presence
tweeter are monopole drivers that emit sound only to front