Yeah, camera is super important to me too. Actually camera and battery life are 2 the most important factors when I choose a phone, just before the display and size.
N4's camera is clearly worse than the camera on the S4(which is the best smartphone camera), it's even behind the S3. Xperia Z comes second to the S4 though, it's the same sensor, just different processing and surprisingly Samsung does that better.
Performance-wise, the N4 has 4 Krait cores. The S4 has newer gen Krait cores which are like 20-30% faster, and clocked a little higher.
Still, I'm willing to bet that the advantage of running stock Android means smoother UI experience and at this point the chipset performance difference is negligible. The chipset performance difference will be visible when launching apps, and it won't be a big jump whatsoever.
If I remember correctly Sofi came from a single core A8 1ghz Nexus S to 4 Krait cores at 1,5ghz. That's like over 1000% performance difference, literally, lol. N4 to SGS4 is like 30%. On paper - that's where the difference is seen.
Xperia Z has very lightweight UI, similarly snappy to stock Android, almost.