2 PSU's... 1 1200W and 1 1000W

And of course 5x Sapphire Toxic R9 280x  Main Specs:  TC=8193, MEM=1800, Engine=1100

As for length of time, I ran for 5 hours no problems with zero HW errors, I rebooted to remove killawatt voltage meter and post pics.

Unfortunately this speed does come with a price, the cards have to run at 1.256V  I can run at 765Kh/s per card at 1.2V if I lower mem to 1500 and engine to 1100.  This also lowers temps from high 70's to low 70's.