I started out with the Xf 250's I had in my 90 gallon transferred into my 210.
Ran them at 70 and 100 % speeds depending on mode used.
Noise at higher speeds is just like any other power head on the
market today with regard to an audible pitch in pulsing modes and such.
Not bothersome at all and just becomes the sound of the home when my tank is running with the skimmer off as the skimmer is the only thing that can be heard on my tank chewing air.
After cleaning them OR when new they tend to make a bit more noise until a good bio film gets in them within a few days to a couple weeks depending on your particular system.
Running them at maxed out speeds and still not satisfied with the flow I bought Two XF 280's and WHAT a difference in flow !!
These monsters are just what the flow doctor ordered. I can run them at 70% max speed in some of the modes but will shift my sand around which does not bother me as a different mode will put it back LOL.
I like to run the preset modes with a min speed of 40% and max of 80% with just the 280's running.
Now I do use the 250's still on the back glass and they are run with the Ice cap modules controlled via Apex for some killer random flow patterns coming off the back glass and disrupting the 280's. The 250's are definitely not needed now that I have the 280's, I just wanted more flow and more random chaos for my corals and fish.
If you are one that thinks corals will be ''hurt'' from tank flow then get the 250's and run them at 50% or less
If you plan to have corals grow out into mature colonies that need high flow rates then get the 280's
Word of advise, the 280's can NOT be controlled with the Ice Cap interface modules so If you want third party control then stick to the 250's and if two are not enough for your tank needs then you can always purchase a third and run it off the native controller for a while or get another GIM.