I built my router in 2006 and have run it hard since. Built from 1/2 ply, I used torsion box construction so my rails are well supported. I have very few problems with the machine warping. Skate rail x and y. And v bearing on the z. Skate rails work great! Just be sure to get sealed bearings, not shielded. Over the years shielded will get crammed up with dust. I have had it to as much as 250 in/min but best cutting is at 30-40 in/min si I keep the rapid at about 150. Cuts about anything including AL at slow speeds and light cuts using woodworking carbide bits. The v bearings seem to work great on the Z.
Skate bearing and ply works great for me in a router and true linear bearings are just a waste of money.
Dave