First things first: the Radeon HD 4770 is faster than existing 4800 series hardware (namely the 4830). Yes, this is by design.
We hate to start another article complaining about naming (there seems to be some sort of pervasive renaissance of poor naming this year), but let's talk about why exactly we are in this situation with a look back at something from our RV670 coverage:
At least it's ironic.
Yes, the problem is born out of AMD's attempt at sensible, appropriate naming.
The problem is that AMD seems to want to associate that "family" number with the physical GPU than with the a performance class.
This is despite the fact that they generally use increasing numbers for "families" that are generally faster.
You can read the rest of the article over here