I'm suggesting that you don't bother with the echo test you described (unless you're trying to make the best of a congested network link) because it will be a waste of your time. On the other hand, if real human beings you call have been reporting a slightly awkward delay between the time they say something and the time you respond, you might consider reducing this setting to see if it helps.
I have never heard of 0.030. being incompatible with g.711u. It merely means larger RTP packets (and fewer of them per second) than would be sent with 0.020 or 0.010. Fewer, larger packets yield more efficient use of network links due to less overhead data. More, smaller packets yield slightly less latency between speaker and listener.
