Make sure you balance your rear gear with the 1st gear as well. Multiply the rear gear times the 1st gear.
For example: lets say you had a 69 Camaro with 4.11s and a Muncie Rockcrusher for a baseline. Take the 4.11:1 rear gear x 2.20:1 first gear = 9.04:1. That's a good benchmark for a performance oriented 'Starting Line Ratio' or 'Total Mechanical Advantage'. Anything from 9-10:1 is useable comfortably on the street. If using an aluminum flywheel, you may way to hedge closer to the 10:1 mark or more.
Do you have the 'close ratio' or wide ratio TR6060 (sold as the "T56 Magnum")?
Close ratio would be the 2.66 1st gear, and the wide is (I think) 2.97. If you have the CLOSE, I would run at LEAST a 3.73; up to say a 4.56. If you have the WIDE, run something like a 3.73. What you don't want is a first gear thats too deep to be practical. Guys who miss these kinds of things end up with a 6speed that becomes a really big 5 speed because they either dont have enough rear gear to make 6th useable often, or a tractor like 1st gear thats useless and they usually start off in 2nd. A lot of this depends on your driving style.
Contact your engine builder or cam manufacturer and find the cruising RPM for your combo; target for that, ESPECIALLY if carbureted.
Footnote: as I mentioned earlier, the 'T56 magnum' is NOT a T56; it is the current generation 6 speed (called the TR6060) produced by Tremec and sold by their North American counterpart as a crate transmission. Write down the Tag Number on the gearbox (something like TUET7744 or TUET11009) as this is the only way to get parts and service for one should you need it. If you don't know what ratio's you have, post the tag number and I'll gladly look it up for you.