Four-hundred mg is generally as high as most doctors will go (as per the PDR, I believe), but I've known people who were prescribed on as much as 450 mg.
Going higher than this recommended limit increases risk of seizures.
Your doctor also needs to assess your general medical condition, any other meds that you may be on, etc.
My personal experience is there's no difference between generic and brand-name, aside from cost (and co-pay).