Has anyone done any tests or seen any tests by actually cutting down a 26 inch tube inch by inch?

Only ones I remember were with .308 & .223 I think.

It is about 25 yard/1"

no but comparing velocities from having a 22 inch, 24 inch, 26 inch and 28 inch barrels on 4 different 22.250s..... the longest barrel definitely gets the most velocity from the same load...

one load I use for example gets only 3200 fps out of the 22 inch barrel...but gets 3500 fps out of the 28 inch barrel..

since it is a low pressure load ( 5 grains under Max..but very very accurate).. It is easy on the brass so I use it in the 28 inch barrel..

the 28 inch barrel is adding about 300 fps MV over the 22 inch barrel...this doesn't fit the accepted norm...but it is what my rifles give me anyway...

Saeed had a link to someone who did just what you asked about a month ago. I believe it was with a 223 but hell I can't remember for sure - could have been a 416 Rigby.