A comment on sound:
With the additional mass of the 4th axis to move around, my 'X" axis started loosing steps occasionally, so I am planning to replace it with a servo motor. Until I decide which motor I want as a permanent replacement, I replaced the 425 oz-in NEMA23 (parallel wired) with a 640 oz-in NEMA34 (series wired) stepper that I had left over from my 4th axis project. Gecko 203V drive @ 72V.
http://www.kelinginc.net/SMotorstock.htmlWhile I have not done any performance testing or run any parts yet, I can tell you that the difference in sound is extreme.
The NEMA23 was a screamer and the NEMA34 is almost as quiet as a servo. So my little Fankenmill currently has a NEMA34 on the 'X" and the NEMA23 on the 'Y'. With a program running, all you hear is the little 23 motor screaming away.