my prius is so oddd....

I think OP is miscalculating the mpg of the Prius versus the BMW 328xi. I think the 44.9 mpg for the Prius sounds about right for the way OP drives, and I think OP must be getting that off the MFD. But I think OP's gas station fill-ups don't sound right, and OP's mpg calculations for the BMW are way off.

My conclusion, is that OP averages 44.9 mpg with the Prius on regular gas, and 20 mpg at the very most (this is average EPA figure for the BMW using the EPA's 2008 method) with the BMW on premium.

So the Prius uses regular while the BMW uses premium. And the Prius uses much less than half the gas of the BMW, and has far fewer emissions. I think OP should consider getting rid of the BMW, not the Prius.

 

sounds like the OP is tired of the prius and just wants another vehicle.