In addition to the seat width, so other points to consider.

Going thru GRU puts you in the new T3 and able to use the new *A lounge which is very nice. GIG has the SMILES lounge (former Varig as you likely know).

The 2-2-2 777 has a small divider on the arm rest betweeen the seats. Doesn't prevent cponversation with your wife, but makes it difficult to hold hands if you like to do that.

The foot rest area on the 2-4-2 777 is larger than on the 2-2-2 777 with the possible exception of the bulkhead seats on the 2-2-2 777.

I believe the seats on the 764 are the same as on the 2-2-2 777. Someone who has been on it can correct me if this is wrong.

I like the AVOD system on the 2-4-2 777 better. Also, you can lower one of the arm rests which can give you a bit more room. I find these seats more comfortable than on the 2-2-2 777. I also concur with others that facing backward is not a problem. In fact, I prefer it. It is also deemed safer. I have flown on military medical transports and all the seats face backwards for that reason (so I was told).

You don't mention your onward connection, but I would think going thru EWR would be longer overall, yet it will yield more miles.