There could be several explainable reasons why Stitch felt that the X5 was more powerful, she mentions them above, but I would like to expand on it:
- Automatic transmission programming - It's almost certain that they do not use the same program and perhaps automatic transmission, and things like clutch pack engagement, torque converter lockup, etc. have alot to do with the "feel" of a vehicle.
- Tires - brand, compound, and most importantly inflation. For all we know the X3 she drove had soft, squishy, under-inflated tires.
And she did say it was "a feeling from her waist" meaning that it was a subjective opinion....