Geometric clock on 7900GT's

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Ive been wondering why the geometric clocks are clocked differently on some cards some have +20 and have +50 mine personally comes with +20 ( inno3dbrand ) and im wondering if increasing its delta value to 50 or more would improve performance at a noticable level also removing the delta value didnt allow me to overclock past 615 w/o artifacts in ATI tool, as of now i reflashed my bios to give it a delta of +50 and it seems to be doing fine under 615Mhz core

EDIT:
Also when flashing with nvflash are there specific flash commands to use aside from the -r