I definitely wouldn't go for a model with 2.5x less airflow, even if it's near silent. You're asking for trouble...
You may have something wrong with the fans, they are supposed to be regulated, I can barely hear them.
By the way I have now 7x1.5tb (wd15eads) in the n7700, and the temp is 35-37 during RAID build (so max stress). It's closer to 27-28 idle.
I had 8 reallocated sectors on one of the drive just after formatting the raid the first time, and it dropped out of the raid (I had activated TLER on all drives). WD diag says it's fie, so I'm reformatting now the 7 drives, hoping the sector count is not going to grow (I'm raid6/xfs so it should be fine if it does).