If you're on a 3 class 777, 6A is the best seat in my opinion (better than 6K if you're right handed and want to constantly drink champagne )

I'm not sure how you were able to change to a seat in row 5 - it shouldn't exist if you're on a 3 class. Also see if you can get row 1/2 as then you get an F seat (if they aren't selling F class).