I'll start with a bit of background. I have an RF-45 style mill that i'm planning to CNC over the next few months. I've got ballscrews and am converting all the axis at the moment, planning to drive the head rather than the quill for the z axis. Probably going to go for a 2:1 reduction on the drives.
On to the drivers... I was thinking for this size mill I should use a Nema34 size stepper, I can't afford to use servo drives at the moment and it's only a hobby machine so I think it'd be wasted too. I've narrowed it down to a digital driver, now do I go for a leadshine EM806, DM870 or the Kinco 2M880N? They are all similar priced at about £100 a piece from Zapp or Motion. The other option is a CWD 872 from cnc4you for £66. I guess my question is are the other drivers worth the extra or will I get good enough results using the cheaper?

I understand the impedance should be used to calc the running voltage. I have seen 34 motors with 6-8mH per phase and approx 8Nm so this would give a voltage of 78-90V based on the square route(impedance) x32 from the gecko drive site. Does this sound right or should I double the impedance as two phase? I would be running at 70-75v as the drivers are only 80V so would loose some motor power and speed. I could however go for a 23 size motor producing 4Nm and gear down further to get the torque. This motor could run at 60v and achieve almost maximum performance.
What do you guys think?

Sorry for all the questions!