Normally, to find power supply size you add TDP of all components and add 20%. Google "TDP 7950" will get you the answer.
Anyway, it is 200W. You need 1000W for 5 GPU alone then, plus another 100-150W for the motherboard and processor. If you overclock you should plan for 225-250W per card even.
So, you need at least a 1100W power supply, but you should buy a 1200-1300W one for better results. Cheap ones are over-rated. Combining them is OK, but be mindful that you load them evenly.
i am sorry my english is not good and i cant know the keywords about something weird for me. like TDP 7950, for example i dont know what is tdp.
thanks for help. i already bought 2 of 750w psu and i think this will be enough. three cards to one psu and two cards + rest systrem to an other psu.
i will try to run with windows 8 and yes i will try to make some overclock and i will try to reduce volt. i think mis after burner will be okey for overclock and undervolt?
thanks.