GPU-Z uses a database to identify the cards. If the DB isn't up-to-date, it shows incorrect information (well, clock rates are probably read real-time). Even the original author of the review says that the GPU-Z values are wrong:

"We test used by the test drive version amd_vista_radeonhd_4850_8.50.3_final_certified, in the latest version of the GPU-Z in a comprehensive manner and failed to obtain relevant information, but we can understand that the core and memory frequencies were 625 / 1986MHz."

So 480vs800 SP is still undecided. I would lean on the 800's side though...