You have just a little more room to go up with bupropion. You can go up to 450 mg/day safely. Beyond that increases the risk of seizures without any additional benefit.

Also, you could ask your pdoc about adding sertraline (Zoloft). It's a great adjunct to bupropion because it's a CYP2B6 inhibitor, which inhibits bupropion's metabolism to hydroxybupropion, which is primarily a norepinephrine reuptake inhibitor. Adding sertraline balances out the dopamine reuptake inhibition relevant to its norepinephrine reuptake inhibition, plus adding serotonin reuptake inhibition to the mix. Also, sertraline is a mild dopamine reuptake inhibitor to boot.