Change SPD-EEPROM on RIMM manually from PC700 to PC800
RIMM (Rambus Inline Memory Module) feature SPD-EEPROM to store timing and access data. Most mainboard BIOS read out these data and automatically set values accordingly. As some manufacturers have not spent much effort in programming all values of the SPD-EEPROM, your BIOS might misinterpret values or you just want to override the settings there's no easy way to reprogram the chip.
Kuroutoshikou has a device named USO800 for sale that does exactly what you need:
USO800 can be used to overclock 128MB / 256MB RIMM PC700 to PC800.
USO800 overrides signals on these pins: A52, A53, A55, A56, A57, B52, B53, B55, B56, B57
USO800 relies on settings stored in two Atmel AT34C02 chips, one chip for 128MB and one for 256MB modules.