NEMA34 motor selection for Bridgeport Series 1 CNC

[m_c]

I'd probably go for the 1100oz-in steppers, as the lower inductance should give better performance.

50V may end up a bit too close to max voltage. You have to remember the 50VAC is at rated load, so at no load the voltage will be higher (a decent quality toroid manufacturer should publish a load regulation figure, which can be used to work out how much voltage will rise under load). Combine that with mains voltage fluctuations (officially mains can vary from 216 to 253V, and toroids will often be rated at 230V), and you can quite easily get a higher voltage than you expect.
And that's before you consider the effects of back EMF during high deceleration of motors, which will result in the drivers dumping energy back into the supply and increasing voltage even higher.