RE: Boeing 777-300ER
if you haven't already done so, you might pose this question in the "Jets" forum, to see who else has done the 777. But...
I bet that if you keep it light, and use slotted Fowler flaps, as on the original, you should be able to use the scale wing size. A friend of mine builds and flies relatively heavy models, but uses slotted flaps on most of them. When we first go the the field, he gets a lot of heat about the weight from "armchair pilots", but ALL of his planes take off, fly, and land nicely, thanks to the slotted flaps.
It's easy enough to enlarge the wing later if you find it to be a problem, but if I were building it, I'd start with the scale shape. If it works well, then the fact that it's true scale is just one more bonus you can brag about at the end.
I love Boeing. Please keep us posted as you progress with this project. I'm sure we'd all like to see the process.