I can't actually answer that as I don't have my tank running. I can tell you that two waveboxes in my 280g produced a wave nearly 4" before I panicked and pulled the plug, the wave totally crashed over the side of the tank. The one wavebox produced a wave just slightly under 1".
I don't *think* it affects the overflow significantly, the only thing is if the wave takes the water lower than the overflow waterline, then more water will end up in your main tank until the flow through the overflow equalizes with the flow coming into the tank.
The tanks that I've seen with waveboxes have only had a slight gurgle noise that seemed to coincide with the wave. I didn't think the noise was too bad, but, I dunno, I might be deaf too for all I know.
