Atax stems are in my experience in another league than AVA stems. Some of the AVA stems' problems had to do with being incorrectly specced a tiny bit too small for the steerer, if I recall correctly. Personally I would go for an Atax. Sanding down cylindrical objects is definitely possible, though you need to keep a keen eye on the roundness. If you wind up with an elliptical shape you will reduce the contact area between stem and steerer to a fraction, significantly increasing stress in the stem.