What pitch ballscrew would you recommend?

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Right guys finnaly got back to building my cnc router, gantry is 50" wide and made of 2x6" box alloy and the sides are 20mm thick plate the table is 6ft long and i intend on machining wood plastic and alloy. i have not yet got any motors for this size table and i was going to purchase some of gary's finest ballscrew pretty soon. BUT... im still unsure what pitch to get as i want to have good "nippy" but accurate control over the movement. i have decided to use 25mm thick screw on the X & Y but i could really do with a second or third oppinion on what pitch and motors to get.

I could always add belt drive to the ends instead of direct this might give me some more flexibility..

What do you guys think...