Et street radials on a 4 speed ?

couper
Have you got a calculator?
A change in tires from 26 to 27 is about 4%. At 5500 thats about 220rpm. Thats hardly worth a trip to the track.
The rear change from 3.55s to 3.73s is a change of about 5%. Thats about 275rpm at 5500.

Heres the formula;........MPH= (RPM x TC) / (1056xR1xR2)....

Flipping things around; RPM = (MPHx1056xR1xR2 ) / TC
where TC is Tire circumference; which is Pi x D, where Pi = 3.1416, D = diameter
And where R1 is rear gear, and R2 is tranny gear.
The following is for M/Ts. Autos may/will be slightly higher due to TC slippage.I have no idea of the caliber of your combo, so will just work it out for 106mph in the qt.

EQ1.....RPM = {106 x 1056 x 3.55 x 1.0} / (26x3.1416),Therefore RPM = 4865 in direct
EQ2.... RPM = {106 x 1056 x 3.73 x 1.0} / (27x3.1416),Therefore RPM = 4922 in direct; Thats a 57 rpm diff.
If using 3rd gear, RPMs will be 40% higher using the 3rdgear ratio of 1.40. Unfortunately neither of these gears play well in 3rd at 106 to 111 mph, pulling rpms near/over 7000. To run a 3 gear QT, a 3.23 would play well; pulling around 6000@106. A 4 gearQT would like 4.56s; also pulling about 6000@106.
So plug some numbers in and save a trip to the track.
If you expect 5% more MPH, your RPMs will be the same 5% higher.If you go to 15% more gear, your Rs will rise the same 15%. If you expect 5% more mph AND will use 15% more gear, you could expect to add the 5 and the 15 for rpm and get; 111Mph@5906 using 4.30s over 3.73s.

EQ3; The math goes like this; RPM ={ (106+5%) x 1056 x (3.73+15%) x 1 )} / (27 x 3.1416) = (111.3 x1056 x 4.29 x 1) / (27 x 3.1416) = 5944RPM
the proof is; 5944(from EQ3)/4922(from EQ2) = 1.207 which is about plus 21%! and the estimated;5944/5906 = 1.006 or less than 1% error.
At the track its usually best to use the larger diameter of 2 tire sizes available.The footprint increases faster with an inch of diameter than with an inch of width.The ratio is about 3 to 1. And tire pressures play a huge role in the footprint as well.
Just trying to help.