Hi,
to be honest I agree with peteeng, if you are thinking about 2010 screws do it now. Trying to retrofit larger screws is likely to be a nightmare.
My mini-mill has 2005 C5 screws and while it might be slower than I might achieve with 2010's I sure do like the thrust that comes with the finer pitch.
My new mill build has double-nut THK C5 3205 screws, they are really nice. I'll be running them direct coupled to Delta 750W servos, 3000 rpm rated,
for a max G1 of 15m/min. I can run the servos up to 5000 rpm in 'field weakening mode' for G0's of 25m/min. If I needed more thrust I'd use a planetary reduction,
and seriously even G1's of 15m/min are ANY amount fast enough for a hobby machine, I sure as hell don't need MORE speed. Trying to contain the
acceleration and cutting forces is going to be the determinant (of overall machine performance).....not the servo speed, nor the screw pitch
When all said and done provided you match the pitch of the screw to the torque/speed of the motor who cares? I seriously doubt you'll get anywhere near
the whip speed of 16mm screws....although I'll defer to peteeng's analysis on that score, thus with a fine pitch screw you choose a motor of higher speed but
commensurately lower torque whereas with a coarse pitch you would go for higher torque at lesser speed. In the event both motors will have (near) equal power.
It looks like you are very close to a set of decisions about both the screws and the steppers which will in large degree dictate the accelerations, thrusts and,
as a first guess, cutting forces. You should use those numbers to assess the rest of your design.
Craig