I've seen the Sideshow bust AND screen used hero Iron Man suit in person at Comicon this year. It looked life-size to me. I have one on order and hope they didn't shrink it any. For the price we're paying I'll send it back if it's scaled down!
I photographed both. You'll notice on the hero suit that they put the aluminum "collar bones" on the wrong sides, and rotated 90 degrees from the their orientation in the movie. The Sideshow bust has them correct:
Sideshow Prototype Marketing Photo:
Sideshow Prototype at Comicon:
Screen Used Suit at Comicon:
Still from the movie (CG Iron Man in flight):
At least let's hope that this is the correct orientation