Lol. 3pedals, you must commute around in a homicidal rage seeing you have a demented fixation with how a car handles, but you drive something with the aerodynamics of a cement block and a center of gravity resembling a ferris wheel.
*edit: OP, Go drive both. You'll end up with the extra 2 cylinders - Why have six when you can have eight? If gas mileage was a consideration we'd all be driving Mitsubishi Mirage's and Honda Civics. I can get under 10L/100KM driving like a nana on the motorway, or 16-19L/100KM driving way heavier than we're allowed to on the road anyway. Your e39 will handle fine regardless of either engine, you're not the resurrected Ayrton Senna so you're probably going to drive for the most part like everyone else does. I can steer my old boat around corners and over shitty lumpy NZ roads just fine without falling off it.