I went to a big demo day at a local shop a couple months ago, cast both of these in addition to a number of others.
FOR ME, and my casting style, the Zenith felt like it had a little more backbone, the NRX like it was a little more delicate and accurate up close.
I bought a Zenith 4pc for stillwater, where I want to be able to throw streamers and deal with some pretty stiff wind sometimes.
Later, in a moment of weakness, I bought a Zenith 1pc to deal with dries on streams, where I thought the NRX would have been a better choice than the 4pc Zenith.
Of course, the Zeniths both came to me via Ebay close outs steals.
And that definitely factored into it.
I tried to make it up to the shop buying line and another Lamson though, because I felt a bit guilty.
Hope this helps a bit.