despite only small die size increase (GK104 -> GM204 etc),
This is not true. GK104 is 294 mm2. GM204 is 398 mm2.
I really dont care how big GP104 is.If its not delivering +50% performance on brand new 16FF+ it will be epic fail(vs 970 and 980)
You have to understand, both companies are going to need to milk this node for 3-5 years. Between that and the little transistor/$ cost benefit of 16FF+ over 28 they have to be very stingy unless they want to raise prices by an awful lot suddenly. Don't think that's a good idea.