The backlash will have you pulling out your eyebrow hairs if you have no hair left on your head.
I converted a BP with ballscrews and some pretty large steppers through a 1.5:1 reduction for X and Y and I have been nothing but satisfied. Hell - I still have all of my hair and eyebrows.
My conversion thread is here somewhere, but it's not very well updated.
My stepper conversion costs me about $2500 including the cost of the screws. I went with Hiwin rolled screws and they are really worth the effort - the backlash is less than .0004" each which is very easy to accomodate. The price of the ground screws just couldn't be justified for what I do with the machine.
Once you do the conversion and get confortable with it, you will have no need for manual operation.
Scott
Consistency is a good thing....unless you're consistently an idiot.