I think Danley gave a great answer.
Picture an isosceles triangle with the long sides each measuring 9.5 inches, and the short side measuring 1.7 inches (the width of a fretboard). Now imagine that placed inside a circle where the radius was 9.5 inches, such that the point on the triangle where the two 9.5 inch sides meet, is at the center of the circle, such that the other side cuts a 1.7 inch chord through the circumference of the circle. The distance in inches between the center of the chord and the arc above it is only 0.00956 inches. That represents the height difference from the edge of the fretboard to the middle. If you do the same with a 24 inch circle, using an isosceles triangle with two 12" sides, etc. The chord that is cut by the 1.7 side of the triangle is sits even closer to the arc (0.00753 inches).
Edit: Corrected my math here...)That is a very small difference (.002 inches) we're talking two thousandths of an inch difference in the height of the arc over the fretboard measured from the middle of the fretboard to either edge. I don't care how soft anyone's touch is, most of us won't notice that subtle a difference in most of what we play. Mathematically speaking, even a difference of 2/1000 of an inch in the height of the arc should allow us to to solo better on a 12" radius fret board and chord better on a 9.5" radius fret board. But I think for most of us the distinction will remain mathematical rather than practical.
Depending on tool tolerances (remember we're talking about a 2/1000" difference in height over 0.85 inches (the distance from the edge of the fretboard to the middle of the fretboard), the difference between neck radius may be more of a mathematical target than an actual measurement. CNC machine tolerances are pretty tight, but as their bits are used, they wear down, and tolerances can slip. Fretboards cut when the bits were knew will have a tighter tolerance than the last fretboards cut prior to changing out the bits. That means that depending on the quality controls in the shop where the fretboard is carved, a 9.5" radius could be closer to a 12" than you might expect.
If you find two guitars with identical necks - the only difference being the radius - I don't think many players would tell the difference blindfolded. Likewise if you find two guitars with identical necks and the same radius - but told people one was a 9.5 and the other a 12 - you'd probably get people saying they could feel a difference - not knowing that the difference they feel either represents their own subjective impressions, or maybe even a difference in tolerances when the necks were carved.
Bottom line is, You probably won't notice much of a difference.
Last edited by DanDoulogos on Tue Jun 26, 2018 9:35 am, edited 2 times in total.