Going by later comments that it has not worked, the mini retina and air (being later machines than i have to hand 🙂 ) not being fixed by the reset, seems to do more with the alternative MAC later devices have for connect to WiFi routers.
Not all routers are the same, example, not all have the higher speeds, some older ones are very slow and might be incompatability with old routers, or even the latest ones - tricky do diagnose unless you can exoeriment by altering the WiFi speed and observing tests.
if making the network settings static works, that i assume bypasses this later Apple AIR bespoke option, sending device traffic in and out through 'traditional' ip methods.
APple must patch what ever the cause is pronto, which i'm sure they will so keep a watch for it, meanwhile our joint efforts have at least helped many others, that is rewarding in itself 🙂.
alan