I dont know if the rigidity would be affected but accuracy would be. Also chains tend to stretch over time. If you are going for rack and pinion use helical stuff. I am sure our old small laser at work used to hit 32m/min and this was rack and pinion driven and had great accuracy for a laser cutter. Initial cost might be similar for both systems but I would think that rack and pinion would outlast ballscrews and nuts. The rack is generally a lot harder than the pinion so wont wear very much. The pinions are easy to change being fitted with a key or taper lock or maybe simply a pin through the shaft. Also the pinion wont die if it gets a bit of swarf in it like a ballnut will do. Pinions need to be replaced in pairs when they are changed and you will need a tensioning system to keep them in mesh in the rack correctly.