I've been trying out the Maxx for the past week alongside the S4. I live in a strong area, but running tests side by side with CDMA Field Test and Advanced Signal have consistently showed the S4 has slightly stronger LTE signal while the Maxx has slightly stronger voice signal - but no significant differences. And I can tell you from day to day use, the experience has matched those results. Just for whatever that may or may not be worth!
If you love the photos the S4 produces, I'll tell you now that you won't like the photos the X produces. But they might be sufficient for you given the other trade-offs. So it really comes down to your personal preference and how much the trade-off is worth to you.