Hi, what's the best way to drop 4 GA legendaries?

I think like any other item - choose one in the inventory, click on it, then move your mouse and click again, done!

There isn't a way. It's all drop chance. That's why 3/4ga items are the only things that have any value right now.

thanks for this useful info - would never have figured this out

There is no such a thing as 4ga legendary. Legendary can have 3 affixea only => 3ga max.

Appreciate it, my friend.