Revert "GPU Overclock: GPU overclocking to 487.5 MHz with 5 Steps (400Mhz"

This reverts commit 22a5ad9acb3c0e49c32bf9ddcc1778b3c6171c4d.
Revert "Revert "GPU Overclocking: add 450 MHz option""

This reverts commit e35ae68ae66c90a583c1d930b3b1337b52ae8470.