I would keep the current Southbend lathes and add more if space is available for them since you mention they get backed up. Look at finding more
Southbend or LeBlond lathes. Southbend and LeBlond are what Porter-Cable and Milwaukee are to the power tool world. 10 or 20 years from now you'll still be able to get parts for them.
Proto-Traks are nice too. We have 4 where I work, 1 two axis and 3 three axis machines. Pricey though. You could just add more Bridgeports if that's what you like though. You might even be able to get them donated to the team from local companies, like what we did, as the companies upgraded and the Bridgeports didn't fit thier needs anymore. (We also had a local autobody shop donate the use of a driver and roll back for an hour or so so we could get the machines moved to our location.
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