This is actually a really good point, I know sometimes people complain that they have to turn their volume way up, but does that really matter?? Obviously if your hitting the max point on your volume you may want to reconsider, but going from lets say 9 o'clock to 12 or 1 isn't a big deal. To
@Joe Mac's point, you should do a little experimenting and not get too tied down to what the numbers should be.
For example, I ran my Hana SL at 800 ohms rather than 100 and it gave the sound so much more "air", it sounded wonderful.