6 weight turned up today! Much smiling involved! Only have one 6 weight line which I think may also be a little bit too delicate so that will have to wait.
I only have a 5 weight GT, so I cannot give a definitive answer, but I am going to try it on the 4 since I will be fishing a smallish river/biggish burn tonight that requires fairly short casts. Overlining should let me do this nicely.