Here's some info about how the card performance in 3DMark Vantage on a Core i7 system. As we have already heard earlier this year, the Radeon HD 4770 is just a little bit slower than the Radeon HD 4850.
As we can see, Radeon HD 4770 shows a 3DMark Vantage/GPU Score of P8086/6639, compared with P8367/6891 found on HD 4850, which means HD 4770 only lags behind HD 4850 by 3.47/3.79%.