78G is just a standard isle seat.

81D & G will indeed give you 'guilt free' recline. However as long as you don't recline fast into someone's face, it doesn't matter where you are on the plane to recline your seat. It's not about placement, rather courtesy. Everyone is entitled it recline their seat :P The thing you will notice is people hanging around to stretch their legs and use the lavatories, and light from the galley behind you.

But I digress - I presume you're a solo traveller. I would always try to get A or K seats from rows 71 - 79. The access to the side-bin is really helpful, for me anyway, with all the gadgets/gear I carry!