I use 7 inch resin coated sandpaper on a low speed grinder with 36 to strip paint before bodywork. A flap disk takes it off in a hurry, but a wire wheel is much gentler on the metal. I usually have frames sandblasted though.
Well since someone already bumped this thread, I figure I might as well add to it.
I recently bought a Craftsman Restorer. It's a relatively inexpensive 3" handheld drum sander, and it is friggin amazing for removing paint and rust from square tube and flat surfaces. They have several options for sandpaper drums, plus paint stripping rollers and wire brush rollers.
I bought it to do a unidirectional brushed finish on some aluminum plate for a job I did, but I use it all the time for all sorts of stuff now. It's much faster than a palm sander, and much less aggressive than a grinder. And the vacuum port on it is FAR more efficient at collecting dust than a palm sander.
I'm sure I'll burn it up eventually... It's just a cheap $100 version of a $1000+ surface finisher, but I would still highly recommend it.