Yes, there is pre-check (and a priority line) at ORD. In my experience, all of the lines (Pre, Priority, regular) have always been very short -- by any standard but especially for O'hare standards.

Between ORD and LAX/SFO, VX F is far superior to United: both on-board and (usually) on price. The only downside is the VX schedule is very minimal -- one or two flights a day. That will change in the future though, maybe in 12-24 months.