Radeon HD 3870 isn’t the best card for overclocking, mainly due to rather weak power circuitry. There are ways of working around it, but it requires advanced soldering skills. Beside that, Radeon HD 3870 also suffered from an irritating BIOS bug that made it impossible to overclock the GPU past 862MHz. This could be fixed by flashing the card with a new BIOS, and newer cards don’t need this update, but unfortunately it seems like Radeon HD 3870X2 suffers from the same PLL VCO divider bug. The fix should be pretty much the same as before, but we have to wait for the flash tools to be updated with support for the dual BIOSes found on Radeon HD 3870X2.
