I personally tried running vanilla SHIII on my own noteboook. These were the system specs:
Acer Travelmate 4200
- Processor - Intel Centrino Duo 1.66 Ghz
- RAM - DDR2 1024 MB, 533 Mhz (?)
- Video Card - Intel 950
- Windows XP Home
I experienced a very slow frame rate, very slow loading times, and graphical errors. With GWX, I experienced faster loading times, and I believe the graphics actually loaded better as well. However, I am not sure how this would compare to your system. Your video card sounds a lot better than mine, at any rate.