I have the AWD Magnum RT and I don't feel any pull on the highway. In fact, it feels like any RWD in normal driving.
When you hit a corner very fast, it does have a strange tendency for the steering to become very light. That is the only way I can describe it... if you are in a sharp corner and moving fast, the steering resistance becomes less rather than more... kinda weird.
As far as being slower, it probably is slightly slower from the added weight - just a guess but I would say 2 or 3 tenths at most. I am not sure that the additional traction off the line would make up for the weight. The difference would probably come down to the reaction times between drivers anyway.
Now if you start adding major h.p. with nitrous, blowers, turbos or whatever then the additional traction off the line would probably make a bigger difference as long as the AWD system could handle the extra power/ torque.