Tom A. ,
I've tried to post a comment on your website but I must have done something wrong since it didn't show (and you probably didn't get it ;-) ).

There is this "equation" I have a hard time solving ;-) ... maybe you can help :
--> a road tire tested on rollers is always faster with more pressure, almost always true on the road too though there are situations with lower pressure providing an advantage or at least higher pressure no providing one anymore (and creating loss in grip and traction).
--> most rolling resistance tires tests use the same pressure for all tires (in your case, 120psi from your "setup" blog).
--> Continental and Tour Magazine (2014 tires test) provided some good information on how tire pressure influences RR.
--> most of the time at the same pressure the 25 section of one model (let's say GP4000S II) will show better RR than the 23 section of the same model... again at the same pressure.
--> now what if we take comfort into account I'm not sure the bigger tire is really that much faster or much more comfortable, at the same pressure the 25 tire is harder to compress than the 23, it is also faster. Now for the 25 to absorb vibrations and provide the same traction the 23 does provide at the same pressure, I need to drop the pressure in the 25, do I drop it more or less than the pressure difference needed for the RR to be back to "equal" again in between the two, that... I don't know !

Conti graph shows approximately 1.5 bar difference in between 23 and 25 to achieve same 0.45 RR on their graph.

I need to start doing my own testing at home (thanks for sharing the setup !!!) but if I were to conclude, I would say that if you need to ride at a pressure that is close to clincher or clincher rim limit in order to be safe with pinch flat then going up one size is probably worth it, OR if the roads you are going to use are so bumpy that riding a 25 at 70psi provides a real benefit then same thing it's worth trying BUT moving up one size for better RR in a different case doesn't seem to work as at same pressure you will have better RR but loose comfort and aero or you will drop pressure so won't get better RR and will loose in aero again.

Back to your last tests, what is interesting for me is Attack and GP4000S 23 has similar RR at same pressure, but I would ride Attack with slightly more pressure (1mm narrower, 24mm Attack and 25mm GP4000S 23 on most of my rims) so be the same RR and a bit more aero (at least at low yaw angles)... then there is always what Josh said : less pressure in a tire can give a bit of a better aero profile to said tire... crap... it is getting complicated again ;-))))) .

If you have a chance before me, it would be great to try to different sizes at different pressure. Maybe I could try and measure how much a tire compresses at a said pressure, then measure RR, then adjust pressure of the second tire so that it compresses the same ammount as the first one, then test RR. Wooow sounds like a full time job ;-))))

Let me know your thoughts ! Thanks.