i have fished the Z, BIIX and the Helios (in both the mid and tip flexes) and I own the Z and Helios mid flex in 5 wt. All in all for my 5 wt applications my personal preference is the Helios mid flex. Key words there - "personal preference"
I think I might be able to cast a heavy rig a tiny bit further with the Z than with the other two, but that could be a function of my casting and not the rods. All three seem to have good feel with the BIIX possibly the most sensitive of the three..... All three are light (I think in the hand the BIIX feels the lightest for me, Helios in middle then the Z). All three have good warranties, all three will cast in close (BIIX and Helios were tied in terms of up close casting for me).
If you can find a shop I'd try to cast something weighted on each - that might give you best indication of your preference given what you want to use it for.