Funny you mention the Z-Axis, Alan, I've built a few and found the 8'6" #4 to be a real gem. Then on the other hand I've tried good XP's but when I built a 4 piece 9'6" #5 for nymphing I found out quick it needs a lot more work and attention for precision casting at distance. The One series are overall superior, indeed. In most cases it's only one or a couple rods that stick out, but the One's I tried were all good, IMHO.I'd second the BIIX lacking personality, but compared to the 5 weights in any rod range I have had the opportunity to try the 6 weights are often a bit dead.
One rod that immediately springs to mind is the Sage Z Axis, coming between the faithful XP and the unbeatable 'One', the Z Axis just didn't cut it.
Orvis disappointed me with most of their Zero Gravity range though and didn't really make up for it with the Helios. But I guess many will disagree, preferences remain subjective.