at 110 watts per card(Full load, most times less), you can run 4(3 would be safer) of those and a decent cpu(dual core 45nm to save power) with 2 hard drives and a dvd drive. Would be a stretch but with a good psu it would run. so 2 is not the max.
How many amps do I need on the 12v rail?
My psu currently has 18
@oneshot: Im guessing you work for thermaltake and you get a commission
LOL, you would think so, but, 450 recommended could be a lie..a big lie..so by gettin a 1.5 KW PSU I can be sure I don't like lies. I have a 650W CM Real Power with my 4850. I like to mess around. I've been thinking of getting two 1.5 kw's, Tape/glue one psu to the side of the case then I can turn everything off in my APT so I KNOW, my 4850 will undoubtedly work. I like to be sure.
With 4800 heating problem, do not put more than ONE card or your rig will be a melted choclate
So much BS in this thread. The xml hack will get the temps down to the 50s on two 4850s. The 4850 is both power-efficient and potentially cool-running - if the fan is set to run at 50% or more duty cycle.
As for power supply wattage, when my Antec Quattro 850 failed (Manufacturing defect) I ran two overclocked HD 4850s, six drives, water cooling, and an overclocked Q6600 on an Asus Maximus with a 550 watt Silverstone Zeus supply for a week with no problems. The replacement Quattro is now back in the system and runs cool with the fan not audible during gaming on this rig.