They are a bit different in measurement, but to be honest I feel almost zero difference in playing them back to back. But then again, I’m not very size sensitive since I bounce all around different basses, different brands, different scales and even 4 and 5 string necks.
When looking at these numbers I’d recommend rounding to two decimal places, with the fretboard radius it’s very difficult to be accurate down to the thousandths of an inch (heck, 10 seconds with a piece of 200 grit sand paper will remove more than that). Not to mentioned the 1990 Greco has white paint and clear coat vs the 1977 Greco with wood stain and clear coat.
Keeping that in mind the difference between the two isn’t too much…
1/100” at fret one
1/100” at fret three
5/100” at fret five
Keeping in mind what you said above, and that I have a cheap Harbour Freight caliper, here they are favorite to least (and my ThunderP is at practice):
All-time favorite is the Fender Custom Shop, 1 piece NOS '59P neck, no pain ever
Nut 1.75 #1 .80 #3 .90 #5 .93
Hefner Maple/rosewood, pain after 5 months of heavy home practice
Nut 1.62 #1 .84 #3 .86 #5 .87
Warmoth wenge, never played enough to get pain
Nut 1.59 #1 .89 #3 .92 #5 .93
'66J maple/rosewood, cramping after 10-15 minutes
Nut 1.48 #1 .84 #3 .90 #5 .92
My ThunderP, which is at practice has a 1.65 nut and shallow C profile never causes an issue.
My conclusion is that maybe wide and shallow, nut 1.65-1.75, 7.25-9.5 radius is my sweetspot. The '66J is a narrow D, and the Warmoth is a narrow slightly flattened D. So I guess I am not a Gibson Thunderbird candidate as I suspected. Some Epi Ts? Maybe. Greco T? Maybe