I'd go with the Second Level over a Legacy upgrade in a heartbeat.
Six inches, give or take, is what I would consider the minimum height....but there is some wiggle room in that.
And remember, you're measuring from the top of the bottom rail to the low point of the upper shelf/table/plywood.....not table top to table bottom, if that makes any sense. You need to account for/pick up the height of your bottom track and any roadbed.
Best of luck.
