Dweezilz - and others, who ask for comparison Z3/Z4
I had the Z3 at home for a few days, before I got my Z4 (my dealer was so kind to offer me a cine4home calibrated Z3 to make waiting for the Z4 a bit easier).
Since I gave the Z3 back, when my Z4 arrived, I never could compare them face to face, so take my comments with a grain of salt.
What I remember vividly, though, was, that I could see pixel-structure of the Z3 on my screen (2.40 m wide, seating distance approx. 4 meters). I could see it especially during long pans and on moving objects (don't know why, but it was clearly better visible for whatever reason). That effect is completely gone with the Z4. Even if for example cine4home claims, that the bigger fillfactor of the new D5 panels in the Z4 is not a visible improvement, I'd like to object. My personal feeling is, that the new panels do in fact add to the performance, make the picture a bit brighter, clearer and pixel-structure less visible.
Vertical banding has not been an issue with 3 units I saw in performance - you might draw the conclusion, that Sanyo has a good grip on production quality control compared to competitors, who showed absolutely different production quality.
Out of the box, I had the impression, that the Z4 had a great calibration in "Kino Hell" (which is the first cinema preset, I think, in the english menue, it is creative cinema). For everyday use and for the "non-tweaker", you sure will get good results with that setting. The Auto-Iris behaviour is great there, I did hardly ever notice it.
As for the fan-noise, I have the strange feeling, that the Z4 is a tiny bit noisier. But: grain of salt - I never had the two units sitting next to each other at home. I was so surprised by the silence of the Z3, that maybe, I am just being too sensitive about the Z4 now. Or: the vent of the Z4 is directed more towards my seating position (I sit only 50 cm away from that vent!!!) Or: the frequency-spectrum of the noise falls into an area, where I am a bit more sensitive to... But: the unit IS silent, very silent compared to other products on the market.
The automatic shutter door is a good feature, as well.
Whether you want to invest more $ in the Z4 over a used or cheap new Z3 - hard to answer. For me, personally: yes. Especially because of the described pixel-structure-effects I saw, the great menue and the possibility to tweak the unit a tad more than the Z3.
I hope, I could give you a bit more information for your decision.