I'm getting into more accurate work and worrying the Tormach isn't going to be up to it - so I decided to get some real facts to help with my decision.
I spend some time setting the X and Y trust bearings and gibs to what I thought was optimum - and then ran the following test - see attached Pic and G code.
The roundness was within 0.025 (0.001") total error - checked by micrometer and in lathe with dial indicator. (23.98 - 24.005 mm).
Good news!