I never got to see a "G" operate in real life
BUT, the stories of them flying up and down the Corridor...
The HP peaked at around a little under 9000 for a one hour rating - at 70mph. And fell off FAST after that.
A modern European motor, as bland as it looks, will spank a GG-1 in just about every way. NJT Transit's DB class 101 derivative ALP-46s will break traction at 40mph, especially on wet days. I've seen/heard it. No US diesel can do that, at that speed. None.
But the "G" pioneered the suspended motor design that is standard in the EU, and on electrics in the US. ( I think the new Acela ll have TGV-style body mounted motors).
Then you have the British and the wacky, but oddly successful Class 91 traction motor setup. I did a double take when I first saw it getting off the train at York..