The 7950 is by far the fastest and always will be in DX9 games. There is no Mobility 2600 currently and I can assure you, it will also be inferior to the 7950. You will have to wait a few months before the DX10 high-end mobile GPU's come out... I wouldn't expect much improvement over the 7950 with the exception of DX10 support and maybe a 20% speed increase over the 7950.
Power and Heat is catching up with the notebook segment... You can't just dump a power hungry card into a laptop - battery life is killed and even if one still did it, how are you going to cool it? The laptop would be a monster... So, they neuter the card by lowering clock speeds and vertex shaders along with a host of other options...