the sidereal rate is the rate at which the earth spins on its axis, and consequently the rate at which the 'fixed' stars appear to move in the sky. This is the rate which you must match with your RA axis. The point of an equatorial mount is that the RA axis is set up to be parallel to the earths north/south axis, and spins at the same rate (in the opposite direction) so that it keeps the apparently-moving stars still in your eyepiece.
The focal length of the scope and eyepieces make no difference to the rate at which the earth turns so you do not need to alter the rate of spin of your RA axis. Imagine a snail that always moves at 1 cm per minute. You stick him on the edge of a large dinner plate and point him towards the opposite edge. The plate is 30 cm across, so it will take him 30 minutes to get across. Same snail, smaller plate - 15 cms this time - it will take him 15 minutes to cross. In case you were wondering, the snail is a star, and the dinner plate represents your FOV....
The field of view of your scope will just determine how big a patch of sky you see, and the stars will traverse your field of view quickly if it is a small FOV and more slowly for a larger FOV, but they are still 'moving' at the same speed.
By the way -relative to the stars - the earth rotates on its axis once every 23.93447 hours (23 hours, 56 minutes, 4.091 seconds), so you have to get your motor / gears to turn you RA axis once every 23.93447 hours.
there is a good explanation
here
Hope this helps.
Adam