www.ditl.org

so if you had to do specs on the Excelsior, Miranda, and other starship classes if they were still in the 23rd century, instead of a speed of Warp 8.6 (TNG scale) for the Excelsior for example, what speed would you give the ships in the old TOS scale?

The website has a calculator for that. Also the website has classes with their speed as well. Not official as you can pick something different.