The 9400 mGPU's clock speed is higher than the GeForce 9300 mGPU.
GeForce 9400 mGPU:
580MHz Graphics Clock / 1.4GHz Processor clock / 16 Processor Cores.
GeForce 9300 m GPU:
450MHz Graphics Clock / 1.2GHz Processor clock / 16 Processor Cores.
*Specifications may vary by motherboard manufacturer. Please refer to the manufacturers' website for actual retail product specifications.