I feel so pathetic responding to my own post over and over!
I noticed something odd when doing a backup to the zpool today; the data seemed to be going on the disk in spurts... it would write, pause, write, pause, etc... So I pulled up Activity Monitor and this is what I see:

The write speed is bouncing back and forth between about 80MB/sec and as low as 28KB per sec.
Also, you can see that "kernel_task" running as root is consuming 4.24 GB!!! That must be Zevo CE? There's still over 2 GB free so I'm not concerned about it, just curious.
Does anyone know what might be causing that pause in writes?