Vorta, did you do any fan mods?@
Yes, I have (ended up doing this). 2x Scythe Ultra Kaze (push-pull) has proven to be the best in airflow vs. sound ratio. You'll also be able to overclock your miner.
Push-pull combination will always work better than any push-only configuration on the S5 because of a lot of air escaping the heatsink before reaching it's end. I would recommend not buying Deltas as they are very loud. I would also not recommend overclocking the miner while using only one fan. Unless you have an infrared thermometer to monitor the temperatures of chips in the back of the miner ensuring they don't go over 90°C as you're testing the frequencies.
or smartly... run the fan from the back to the front
Wouldn't doing that just make the other end of chips run higher? Whichever end is further from the fan will just run hotter, no?
True, the thermometer is in the middle of the hashboard so whichever end the fan is on you get the same readout, but the chips next to the fan are colder than the readout, and chips on the back side are quite a bit hotter. The best solution would've been if there were 3 thermometers per hash board, one at each end and one in the middle.