Well there is no guarantee. AMD may be pushing these cards harder than 40nm models. Remember 40nm is pretty mature now so getting yields high is almost trivial which means you have lots of very good chips (more than you can use in the best cards). Sometimes after a die shrink overclocking hits a brickwall until they work the kinks out.
I remember one Intel CPU after a dieshrink that couldn't be overclocked more than 2% without crashing. Intel was selling the chip at almost redline because they didn't have good enough yields to use a better quality chip for that part/pricepoint.
AMD wanted to have it in stores 2 weeks ago. The chips are made by TMSC and they had delays. Nothing AMD could do but watch and see Christmas shopping season vanish.