windows 8.1 vs 7 experience index

[Cnaeus]

Hi,
I recently tried out windows 8.1, and wanted to make a comparison. For that, I used the benchmark called "ChrisPC experience index". Now I ran the experience index on both win 8.1 an 7, with all drivers, directx etc. installed, and the two OS scored nearly identically EXCEPT the 3d graphics performance, in which windows 8.1 scored an awful 4,6 vs windows 7 's 6,6...
what could cause this? is 3d really so bad in win 8.1?
just for the record: I tested this ChrisPC experience index against the original win 7 experience index, and the scores they provided were perfectly identical.
also, I have a Nvidia 635m videocart (with optimus technology)

 

[Nuckles_56]

it is probably because of the fact that graphics cards have improved a lot since win 7 was first written and microsoft hasn't updated the windows experience index to reflect those changes in win7