We have the older generation SL-10 machine. I have seen the ST-10 at the IMTS show in Chicago a year and a half ago. They have made some updates to the machine, but not so much that I would be way off with information here.
The -10 sized machine may be a little small for the parts you are going to be running. Mostly in the drilling department. I run a 1" (25.4 mm) Iscar DR Twist drill in some 4140 steel from time to time. I would say that is probably about the upper limit. I suppose you could go more, if you really push the machine. Then again, how long is it really going to last like that?
Our machine is just about 5 years old and it does not do too bad at holding size. Depending on the part dia., length, material, etc., we have held as close as +/-0.0002" on OD, ID, and length. The machine is old enough now, that on some parts, generally long, skinny parts, roundness is 0.0005"-0.001".
Overall, both the -10 and -20 sized machines would serve you well. I would, though, lean more towards the ST-20 in light of the size of parts and types of material you run.
Good luck in your search!