I made this short video of two Radeon HD6870 cards running in my system.
They are overclocked to 1000/1150Mhz and are running 3DMArk vantage on High Preset, I disabled CPU anf Feature test so no Final Score you can see only GPU Score !
Test system was:
AMD Phenom II 955BE @ 3600MHz
DFI Lanparty 790FXB-M2RSH [16x/16x Crossfire]
4x1GB DDR2 Geil BD @ 800Mhz
Gigabyte Radeon HD 6870 + Sapphire Radeon HD 6870 both @ 1000/1150Mhz.
Testing done on OCZ StealthXStream 600W Power Supply !!! It passed all tests and game benchmarks without a problem even overclocked !
You don't actually need very powerfull power supply and performance are great with HD 6870 !