Dual boot Mavericks, Windows 7 Graphics problem

[Invading]

Hi there

I built following system:

MB: Gigabyte GA-Z87X-UD5H
CPU: i7 4770K
RAM:Corsair 2x8 GB DDR3-1600
GPU's: 2x Gigabyte GTX 780 OC Windforce
HDD: 2x SSD Kingston HyperX 3K 240 GB, SATA-3
PSU: 850W

On Mavericks the Graphics performance is great!
On Windows 7 (64Bit) the Graphics performance isn't that good.
Video's don't run as smooth as they should, also Powerpoint animations are Lagging. So I think it's a Windows problem. Or a problem on how Windows manages RAM / VRAM and HDD (don't know)
Mavericks is on the first SSD
Windows is on the second SSD

I've tried following:
Install older Graphic drivers (a few)
Update Bios from MB
Tweaking settings on the GPU's NVIDIA interface
Total clean installation with newest drivers

All didn't have any effect.
The performance index from Windows tells me everything should be top. Only 7.8 and 7.9 marks. Also the Windows troubleshooter didn't bring anything.

Has anybody experienced something like this? And does anybody know where I should look for a solution?

Thanx a lot in advance!!

 

[Going Bald]

Do you have virtual technology enabled in BIOS (not talking about VT-d - that should be disabled)?

 

[Invading]

Both are Enabled, cannot disable VT-d in the Bios...