I really set the bar way too high for myself this time. Also, I think I made the mistake of basting and quilting it while fresh out of the worst flu I've ever had.
Result = serious, serious puckering and diagonal shear. Sh^t.
Resisted the urge to collapse in a heap and wail, "I'VE RUINED IT!". Finished it off anyway, bound it, attached a label. It's for a friend who has a friend back home with new triplets. He's not picking it up until Friday so I'm tempted to try and whip something else up in the meantime and really make sure I baste this one properly. I don't know what went wrong - I always use a combination of spray adhesive and safety pins - but maybe because of the size of the patchwork pieces and the randomness of the design it just didn't have enough stability in the sandwich phase.
Anyway, C&C welcome on the rest of it while I work out what to do next.