[artem]

Since 260.12.19 (a clear regression) overclocking on 8XXX class GPUs is broken. 270.18 beta drivers also have this problem.

Downclocking works well:

$ nvclock -m 200 -n 200
Requested memory clock:         200.000 MHz
Requested core clock:           200.000 MHz

Adjusted Coolbits 2D/3D clocks on a nVidia Geforce 8800GT
Memory clock:   200.000 MHz
GPU clock:      200.000 MHz

Now let's try to revert to the original clocks (650/900):

nvclock -r
Your nVidia Geforce 8800GT has been restored to its original clocks
Memory clock:   950.000 MHz
GPU clock:      200.000 MHz

NVIDIA driver doesn't restore GPU clock. However if I try to restore GPU clocks incrementally, it works:

[artem@localhost tmp]$ nvclock -n 300
Requested core clock:           300.000 MHz

Adjusted Coolbits 2D/3D clocks on a nVidia Geforce 8800GT
Memory clock:   950.000 MHz
GPU clock:      200.000 MHz

[artem@localhost tmp]$ nvclock -n 250
Requested core clock:           250.000 MHz

Adjusted Coolbits 2D/3D clocks on a nVidia Geforce 8800GT
Memory clock:   950.000 MHz
GPU clock:      250.000 MHz

[artem@localhost tmp]$ nvclock -n 330
Requested core clock:           330.000 MHz

Adjusted Coolbits 2D/3D clocks on a nVidia Geforce 8800GT
Memory clock:   950.000 MHz
GPU clock:      250.000 MHz

[artem@localhost tmp]$ nvclock -n 300
Requested core clock:           300.000 MHz

Adjusted Coolbits 2D/3D clocks on a nVidia Geforce 8800GT
Memory clock:   950.000 MHz
GPU clock:      300.000 MHz

[artem@localhost tmp]$ nvclock -n 400
Requested core clock:           400.000 MHz

Adjusted Coolbits 2D/3D clocks on a nVidia Geforce 8800GT
Memory clock:   950.000 MHz
GPU clock:      300.000 MHz

[artem@localhost tmp]$ nvclock -n 350
Requested core clock:           350.000 MHz

Adjusted Coolbits 2D/3D clocks on a nVidia Geforce 8800GT
Memory clock:   950.000 MHz
GPU clock:      350.000 MHz

[artem@localhost tmp]$ nvclock -n 400
Requested core clock:           400.000 MHz

Adjusted Coolbits 2D/3D clocks on a nVidia Geforce 8800GT
Memory clock:   950.000 MHz
GPU clock:      400.000 MHz

[artem@localhost tmp]$ nvclock -n 500
Requested core clock:           500.000 MHz

Adjusted Coolbits 2D/3D clocks on a nVidia Geforce 8800GT
Memory clock:   950.000 MHz
GPU clock:      500.000 MHz

[artem@localhost tmp]$ nvclock -n 650
Requested core clock:           650.000 MHz

Adjusted Coolbits 2D/3D clocks on a nVidia Geforce 8800GT
Memory clock:   950.000 MHz
GPU clock:      500.000 MHz

[artem@localhost tmp]$ nvclock -n 600
Requested core clock:           600.000 MHz

Adjusted Coolbits 2D/3D clocks on a nVidia Geforce 8800GT
Memory clock:   950.000 MHz
GPU clock:      600.000 MHz

[artem@localhost tmp]$ nvclock -n 650
Requested core clock:           650.000 MHz

Adjusted Coolbits 2D/3D clocks on a nVidia Geforce 8800GT
Memory clock:   950.000 MHz
GPU clock:      650.000 MHz

Aaron, zander, please reopen the internal ticket for this issue.