So I think you are going to be stuck with higher RPM fan's unless you underclock it. And I would monitor the heck out of it if your messing with fan's. They really were not made to be quiet miner's. There are some good mod's people have done on forum to quiet them some though. Going to S3 level fan... I don't think is one I would do.
If I backed off freq to ~400, and put a S3 type fan on my Batch 6 S7.... I think it would still overheat on a day with ambient > 85*F.... But why do that when you can just turn it down to 30% or less fan speed with the stock fans. I would never consider S3 fans on an S7... The S7 needs the CFM.
Do two things:
Create a cabinet that is insulated to house the miner and its power supply. Have a ducted inlet to the front, and have the exhaust ducted directly from the fan to an exhausting source. the further away, the quieter it is. you really only need like 6-8Ft if you are ducting directly to a duct vent.