I have taken up to 600 mg of Seroquel XR. When it became too sedating the solution for me was that my psychiatrist lowered it a bit. That worked. When I really needed the 600 mg, I had no major issues with it.

I currently take 450 mg Seroquel XR (with Tegretol XR and Lamictal) and do quite well in the morning. I'm writing this at 6:30 am (no alarm) on a Saturday and though I'm slightly sleepy, I wouldn't be in 10 mins if I got up and going. I fell asleep last night at perhaps 10 pm. I took my evening meds last night at 7 pm.

Seroquel XR has been the BEST antipsychotic for me in many ways. Fewest side effects, effective at curbing my mania, and relieves my depression and anxiety, too. I'm even able to lose weight at my current dose. I've lost almost 8 pounds on a serious diet in just these last 3 weeks. Right now I weigh the same weight I was at my highest weight BEFORE ever taking a bipolar medication over 16 years ago. Soon I'll be less than that. I've been this weight even on 600 mg of Seroquel XR.