I'm having a problem getting my head around all this now.
I originally thought the first poster was wondering about the difference in handling. Given that the R is some 257.5lbs heavier and has the benefit of AWD, one would think that adding some extra weight to the rear would change the cars handling somewhat (that's my perception anyway). I've had a number of rather quick cars in the past...some handled well, others not so impressive....adjustments to weight placement helped in some cases. Most notable was a VW Beetle to which we fitted a fully balanced, blueprinted motor and a few other 'goodies',which added about 25 pounds to the curb weight...you could lift the front wheels off the ground from a standing start and suffered from chronic understeer, especially if you tried to power on through corners! A dose of the sandbag treatment stopped all that! We ended up bolting a steel plate to the floor of the front luggage compartment. That was a great car...until some krunt stole it.