I have tested some Matrix Platinum Single / SLI during the last days / weeks also and would say following:
(stock) air:1000 MHZ in all benches - 2/4 cards
1 maxed around 975
1 maxed around 990
water:
not sure, I am not a watercooler (please let me alive
😛 )
I would expect 1050 on most cards with enough voltage (maybe not allday...) - 1000 MHZ almost sure
LN2:1550-1600 in 03 almost guaranteed - 2/3 cards I tested with stummerwinter did 1650+ in 03...still holding up for the best single card score in 03 on GTX 580
😄
Stock coolers usually do a good job until 1.3V, it gets critical then when raising the voltage even further on nspector or similar tools that change VID. always be aware that 3D and 2D voltage will differ A LOT when pushing the buttons on the PCB.
Here is some Unigine Heaven DX9 which even owns 7970 2x, 3x and 4x...old benches do not scale well with more cards....when you mostly like "sub dx10 games" you will have another 2-3 years fun with 580...

I hope my 3930K will do 5750+ then I will be able to finally hit 200k in 03 -.-

And some....uhhmmm...pix
😛

First benching, then baking
😄 😄 😄 
now benching on: LN2 | 3770K | Maximus V Extreme | 2x GTX 580 Matrix Platinum | SSD | Cooler Master 1500W
Proud to be ASUS PowerUser!