1) 20ms is not high ping rate with wireless
2) Ping is just not reliable test on wireless in the first place. You might observe 200ms of latency from times to times. It depends on how much the client is sleeping and prioritizing ping (which is often very low priority compared to sleeping).
So the fact that you link this with upgrade is, to me, a pure coincidence. During a real activity, the client PC will sleep much less and latency will be better.
