OK, replying to most of this...
@Shon31/Latexxx re 2-pass vs crf:
A 2-pass encode at the same bitrate as the crf encode (which varies the bitrate as it goes along to hit a quality goal) looks essentially the same. Doubling or quadrupling the bitrate made only minor differences to the blocky areas, maybe the big groups of blocks got 10% smaller.
@Latexx re resized encode:
I did a resize to 1440x1152 before encoding, then compared it to a 720x576 encode resized after encoding. The block structure is still predominantly the same, which indicates that the blocks are predominantly in the MPEG2. The result does seem a bit less crinkly around the edges though, which suggests that x264 is adding a little mischief of its own, on a smaller scale.
@MugFunky re not using any CQM:
That's what I was doing at the start. Sharktooth's CQM has helped a little with blocking (it is, as I understand it, specifically an anti-blocking matrix). I do do the occasional "control check" with the x264 default matrix, and it's not a lot different.
@Smok3/Revgen/CAFxX re monitor cal:
My monitor is very carefully calibrated -- I'm a photographer and I use it for proofing. Never mind Adobe Gamma, I own a hardware calibrator that measures test patterns on screen.
I see what you're saying: by using the full luminosity range of the monitor to get a punchy and revealing picture, I'm revealing flaws in that picture. Sure, I can squash the picture to hide the flaws (I've tried this), but then I hide the good stuff too. The key point here is that the blocking did not bother me on the DVD because it was hidden by noise/dither (unobtrusive at a suitable viewing distance). But the blocking does becomes a problem on the x264 encode using the same monitor setup, whether x264 reveals it or creates it.
Thanks for all the help and suggestions, everybody.
@*.mp4 guy
You're next, when the queue clears.