Following up on this thread, as promised:

In the interest of science, I walked each economy cabin on both configurations, casually leaned against the wall, pretended to be doing some stretching, and using the extremely accurate measure of "the length of my shoe" was able to estimate leg space.

On both flights, I had about 50cm (1.65') worth of leg space. Being I'm quite tall (193cm / 6'3"), this was not enough for me to stretch my legs but it was just fine to slide down comfy into the seat and have plenty of space to wiggle my knees or sitting with one foot resting on the other knee or something. The one thing that bothered me was that some people felt it was perfectly reasonable to use it to cross over to the other isle.

Regarding the 77B configuration:

• I sat in the middle section of row 41, and would book this again
• Row 60 has about the same space, and is not near the toilets so preferable to some
• Row 31 has about the same leg space, I don't recall why I didn't previously list this option in the #5 post
• Exit row 40 looked fantastic

Regarding the 77Y configuration:

• I sat in the middle section of row 34, and would book this again
• Row 48 has about the same space, and is not near the toilets so preferable to some
• Row 31 does not have the same leg space. While more than usual, I wouldn't pay to book that.
• Exit row 33 looked fantastic

Hope this follow-up helps someone, one day, with picking a seat in economy on these configurations!