[IceFire]

An OS change isn't going to have any effect on the flight models so basically the only thing that it could be, as SaQSoN points out, is input related.

Do you still have Windows XP available to you (i.e. is it an old system). Why not do a test run with a stop watch and see how long it takes for the Corsair to accelerate to top speed at sea level using the same testing methodology. Between the top speed reached and the time it takes to get there should give you an indication on if there is an actual change or not. It may also help zero in on what exactly appears to be different...again something as simple as the joystick sensitivity settings requiring an adjustment may be it.