I have been flown the 737-700 (a.k.a. 73G or 73W) in both C and Y, but not the 772.

Best seats in the 73G Y cabin are 10A and 10F, on the emergency exit row. There are no A and F seats in row 9, thus plenty of legroom. Row 5 is the first row in Y, there is a fixed bulkhead, so I doubt that you can stick your feet under the C class seat in front of you. Check out this thread for a full report on my KQ flight experiences, as well as those of other FTers.

Seat 3C on a 772? I have been told Y class starts at row 10?

When are you flying, Cris? I may have an opportunity to check out the KQ 772 in a couple of weeks, and could report back.

Johan