The devs would have to ask their QA staff to provide the testing results for these things. The devs use only a certain configuration of computers for work, they probably do not recall what performance goes with what hardware off hand.
However, the QA staff and others have a non disclosure agreement they have signed, which means that only certain people on the Paradox staff can release certain information from the testing. As for whom that may be, the person that updated the recent minimum requirements on this forum would be the closest to that level of authorization. An Alternative is the stream manager for Paradox, he would have the technical background and experience testing Stellaris on various platforms, but most of his platforms would be stream capable, meaning rather high end performance wise, not low end.
It's sort of a catch 22 in a bureaucracy.
I concur with Jaol's point. Ever since CK2's version of Clausewitz as far as I know, there's been 3d models and textures in the game, but they haven't done much with it until they modified the engine to produce many new graphics effects for Stellaris.
It takes a certain amount of cpu resources to handle a performance gpu. When the gpu is heavily taxed, I expect the cpu to be under additional load and thread processing as well.