I doubt the sheet metal is going to do much for you in an accident. I think it'll depend more on the reinforcements inside the sheetmetal and the design of the vehicle. I'm pretty sure I've read that our ('90) Trackers don't do well in head on or front corner hits because they crumple pretty deep into the passenger area. I haven't read anything on a side hit, but again, I think it'd depend on the design/strength of the supports inside the door.
FWIW, my 1955 Chevy pickup took a T-bone hit at ~40 MPH hit from a full sized station wagon. Fortunately, I was alone and the hit was into the passenger side. There was about an 8 or 10 inch footwell between the door and the main floorboard that was gone after the hit (I think the frame stopped it. The sheetmetal (pretty thick stuff as I recall) was torn open and the gas tank (behind the seats) was dented
The truck was shoved sideways about 30 feet into someone's yard where the driver's side hit a small tree. As it came up over the curb, the rear wheel was bent almost 90 degrees. I wasn't able to get it out of gear so the driveline stopped short when that rear wheel spun into the frame; that sent the trans & engine forward, pushing the fan through the radiator. Long story short, it was a hell of a mess, but I walked away with just a bump on my head (no seatbelts, so I went airborne and came down facing the driver's door). Anyway, had someone been in the passenger seat, I think they'd have been hurt pretty seriously. So, FWIW, I guess I'm saying I still think the door reinforcement (which probably didn't exist in '55) would be the determining factor in how well a vehicle can take a hit, not the sheetmetal.