Here's my experience with the 2 S5's (batch 2) I received yesterday. Got it unpacked and hooked up and turned on I thought "Oh, hell no!" No way those fans can make this a home miner unless you're talking about keeping them in the Silence of the Lambs basement. Switched to the Silverstone 141 fans on performance mode (1,920RPM is a loud woosh over the scream of the OEM fan) and put them in the back in a pull setup. Turned on and they quickly shot up to 79 degrees Celsius, tried at 312.5M and they stayed at 79. Turned them off and moved the fans to the front (fits fine if you use a bootless network cable) in a push setup, turned them on and they started going up past 70 again, so set the miners at 312.5M and waited. They settled at 70-74 degrees C according to GUI, in a room that's about 75-80 degree F with 0 HW errors. I can handle that, each is hashing about (1,025 GH/s avg.) that's about what my C1 did (1,005 GH/s avg.). Need to get some readings with the Kill-A-Watt today to see how much power it's drawing at 2 x 312.5M.
Here's a little update, so at night the room with little ventilation would get too warm (in the 90's F) and the miners would get too hot, so I added a pair of these fans
http://www.amazon.com/gp/product/B0078IWSBG/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1 that run at 1,320RPM to the rear in a push pull setup and it drops the temps on the S5's down 4 degrees C. Wanted to go with another pair of the Silverstone 141's but the case they're in won't allow due to space so these fit and work well with the 141's in the front and these in the back.
Upping the freq. to 325M on both brings the Gh/s avg. to about 1,070 ea. (about 1,050 avg. on the pool site) and the wattage at the wall on 230v to 1,100w with temp. at about 69 C (in a room at about 83 F).
