I'm looking at linear rails for my x axis (which is supported by my y axis), but the only thing it's gonna be carrying is a 5 inch aluminum collimator (might be replaced with 2 lens mounts instead of one big heavy tube) and a mirror with tilt. I've seen plasma cutters that have a lot of baggage on one tiny little rail, so I'm just wondering how much I can put on one linear rail and still do 200 IPM and hold down .001 at the top and bottom of the carriage, which will presumably be around 7-8 inches high, so figure magnify whatever slop is in the truck by the 3.5 inch overhang.

Modern rails can take massive torque loads. I have seen a home made router that milled wooden doors every day with only one rail and one wagon. Okey, it was a fat THK rail, but even the smallest one can resist a lot of power.
And if you're not going to cut anything, one is good enough.

How small could I actually go? Like are the IKO LWL15s alright, or do I want something more around 25 or 30?