"Wow, the ZX5 over a phoenix wedge. I have not owned the Phoenix wedges, I own the Phoenix tops and they put out, I love them. I wondered if the Phoenix wedges would have a tendency to be top end heavy with the dual horn setup."
Do you really think a loudspeaker designer would design a product with exagerated HF response ? The sole reason for dual drivers in this application is increased power handling. Look at the EV frequency response graph:
"I think I may try a pair of the of the ZX's, now I just have to decide if I want the 12" or the 15". ..... I have read on these forums and it seems some people feel that 12" is the way to go and some feel 15" is the one size to own if you want matching inventory."
Many people, including myself, prefer 12" cones in multiway systems where this driver crosses over into the HF driver. With such a transition the 12's simply sound better. There are exceptions but usually these are systems that are actively processed such as Meyer's CQ-series. Having said that, the Zx5 sounds very good considering it uses a 15".
I do not know (yet) how it compares to the Zx3 as far as the woofer (and its relationship to the HF driver) issue.
"Since these are going to be a dual purpose box, a 15" seems to make more sense? These will be used with a dual 18" sub."
15" certainly makes sense if these are to be used (at times) as a wedge with drums and bass sent through them. They also make sense when used as FOH for gigs where subs are not being used. In other words: they handle more low end.