Gearing is too high on the manual box with 5 ratios, so I can only imagine the slushy with its stupidly high gearing really struggles to get off the line. And that's not considering the power loss through the torque converter, and slower shifting speed etc.
Even the manual 3.0 MV6 ain't particularly quick off the line, it's too heavy and the gearing is too high for the peaky 24V engine. At higher speeds yeah it'll keep up with most things due to good aerodynamics, less influence of weight, and easier to keep the revs in the power band (i.e over 4500 RPM).
I've managed an indicated 0-60ish in my manual MV6 in the low-mid 7 seconds, but that's caning it in a way the quoted figures don't (i.e. dropping the clutch with some significant revs going), so is to be expected. But there are a lot of cars out there that'll match those times, and I can't see an auto getting close seeing that you can't get the revs up until the car hits about 30 MPH.
They ain't sports cars unfortunately 8-)