I'm trying to figure out how you're using that 6" x 1/4" CRS for bearings, but maybe that's a typo. In general, you'd want to use something smoother, like hydraulic piston rod. And over the distances you're talking about, supported rail will work much better than rod that's hanging in the air.
It's hard to talk about your gear reduction without knowing what's being driven, but if it's a leadscrew, you shouldn't have to do that. Steppers don't go too fast as it is, so you want to avoid trading speed for torque if you can avoid it. Especially if you're cutting wood, you need that speed to avoid burning it.
In general, for bigger machines, you'd use bigger motors. I'd vote for the first plan over the second one. The 203 drives can take more voltage than the ones in the G540, so you'll get better speed out of the motors, all things being equal. Servo motors and G320 drives might be an even better choice. Servo motors go a lot faster than steppers, so you can gear them down without much downside.
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