All Corsair PSU's quality wise are excellent. But when it comes to running two 4870's the primary concern is output. Right now just looking at the web which the cards operate in 2D the current load from my system is 428 watts. Thats two 4870's, sound card (requires power from PSU), 4 hard drives, one optical drive, three 140mm fans and a waterpump. Now start up a game when it kicks in 3D and draws peak loads 620 watts isn't gonna cut it and my 4870's don't draw power for fans there watercooled. Like I said before you have to concider all the other power drawing sources. You can never have too much power but a lack will cause many headaches.