I personally would stay on the 777 with the NGBC seat. The seat on the 767 is just so narrow I don't find it that comfortable for sleeping, and I certainly wouldn't pay a premium for it. I've never had too much of a problem with the angled NGBC seat personally, especially the 777 version.

Just out of curiosity, what's the buy-up to F cost on the 777 flight? If it's within $400-500, I would say that's the way to go.