Curious to see what the tallest working robot made in vex is as Karthik really emphasized the no-height limit for the robot at the reveal of In the Zone.
I'm sure this won't even come close to the tallest, but the robot I'm messing around with these days extends up to about 56 inches. It's a competition-legal robot, but it won't ever compete (I'm a little old for VRC and I'm not enrolled in college...)
I'd have to say it'd be a robot from Skyrise. The Skyrise towers themselves were 5 ft tall at the highest, and many robots would lift at least one 8 inch cube over the top, coming to a minimum height of 68". Off the top of my head, I'd say it was Disco's DR6B, but I'm not sure.