overclocking of Gainward 8484-Bliss 8600 GT

[D.Watzke]

I just bought a new graphics card - Gainward 8484-Bliss 8600 GT (Golden Sample). In every review and discussion you can read about stable overclocking (from 600/1600) to 700/1750 MHz and so. I tried to overclock it and it goes crazy even if I try only 650/1600 MHz. Artifacts sometimes appear even if I set clocks back to the default after while. This is weird and I think it may be a driver-related issue. What do you think? Anyone else with this card? Could you please tell me if it runs stable at higher clocks for you, please?

P.S. Card's temperature is OK, I haven't seen more than 56°C. I'm using v100.14.11 drivers. Running Gentoo Linux (~amd64).