I know I am super late to the party, but for what it's worth I would certainly purchase a GP40-2 if they offered one. Any phase is fine. These are more attractive than the SD40-2, because in O-scale I prefer 4 axle diesels. Perhaps I'm not alone in that?
In HO I have built and detailed every phase of GP40-2, which was a lot of work to be accurate! Although I could do it again in O-scale, I would prefer to just purchase a factory one if available. Maybe two!