if sending to broadcast I experience 200ms pauses every 100ms.
I found in reply #3 here http://forum.arduino.cc/index.php?topic=316443.0 that this might be related to sending to multiple IPs.
In fact sending to a specific IP cause the pauses to drop to 5ms (still occurring every 100ms).
this behavior is independent from: CPU frequency 80/160MHz or sending interval 1ms/2ms/4ms.
I'm diving into lwip looking for hints but that is going to take time.
Is this 100ms interval some UDP specification?!
what would you guess is happening during the pauses?!