I'm not sure how the physics are modeled but you might find that your new CPU/GPU has more 'maths options' (MMX/XMM/SSEx and whatever's on the GPU) to choose from, as compared to XP on the older laptop.
If the game is using these options for physics calculations, and its different to what it was on your old XP laptop.. the results will be different. What you getting now is probably what the devs intended the physics to be like.
A slight adjustment in your flying skills would help you re-enjoy the game again.
