None of these affects performance. Instead, they affect how the picture looks on your display.
I have no idea what that ITC processing is, I have no such options. I suggest reading the help file for information about that.
GPU scaling is meant to make sure 4:3 resolutions aren't stretched on your wide screen. If you enable it and set it to maintain aspect ratio, you'll have black bars at the two side of the screen when running in a 4:3 resolution. This is called pillarboxing.
There is also an overscan setting, which should be set in such a way that the picture fits your screen. Usually it's at 0%.
CPU: AMD Phenom II X4 810 @ 3250MHz | RAM: Kingmax 2x2GB DDR2 800 @ 833MHz| MoBo: MSI K9A2 CF v1.0 (BIOS: 1.D)| GPU: Asus HD 6850 1024MB (DirectCu) @ 850/1150MHz | Display: L24FHD | PSU: PC Power & Cooling Silencer 750 Quad | OS: MS Windows 7 Pro x64
CPU: Pentium 4 Northwood S478 @ 3200MHz | RAM: 1,5GB DDR 400| MoBo: Gigabyte GA-8S661FXMP-RZ | GPU: ASUS Radeon X1650 Pro 256MB | Display: Dimarson 19" CRT | PSU: Noname 400W | OS: changing twice every week...