Gathered these numbers around the net, so use them only as a guide.
Power consumption of AMD Cards4870 160W
4890 190W
5850 150W
5870 190W
6950 160W
6970 210W
If your PSU is 80+ then its true output power can be calculated by the rated number multiplied by 0,8. From a 750W rated PSU, you will most probably get a true-600W of power (750*0,8).
...or you can use this
http://extreme.outervision.com/psucalculatorlite.jspI thought it was calculated the other way around? It should provide 750 watts of DC power. Due to inefficiencies, it will draw more AC power at the wall and expel this inefficiency as heat. 80% efficient 750w psu at full load should output 750w of DC power and 150w of heat (900w AC power)
on topic though, to respond to OP, yes 800w PSU should be well above and beyond what you need for those two cards. If it is a single rail PSU, you are golden and have huge headroom, enough to porbbaly hook up 2 more cards on top of that. If it is multi rail though, you might be screwed, as you will have power "locked" to certain rails and unavailable to use to your cards. I have a 550w PSU thats multirail, and it refuses to power any more than 2 5830's severely undervolted and underclocked without turning off. I also have an old 20-pin ATX 600watt power supply that will happily power 3 cards at normal speeds because it isnt multi-rail
Multi-rail is bad, it provides too much hastle and problems with balancing load. Single rail PSU's you just plug in and go, no problem.
