I wouldn't mount an articulating 50" to metal studs at all. period. Even at 16" spacing. The issue is that any kind of lag/screw can tear out of the metal stud with that kind of weight.

Having said that, one idea might be to open the wall, somehow THRU-BOLT 1" plywood to the metal studs, and then re-cover the wall and lag into the plywood. ...Barring that, you are better off using as many Togglers (the brand, NOT toggle bolts) in the drywall as you can and make sure your insurance is up to date!