My general findings for FreeNAS 11.1 in general and on an N40L or N54L (by far the most popular home NAS setups among my friends) are:
- the minimum recommended 8GB of ECC RAM is plenty to safely run FreeNAS and saturate 1G networking for bulk storage purposes, 16Gb is needed to saturate 10G networking, and 32GB (not possible in most of the HP Microservers) does not give much of an advantage over 16GB in the large bulk transfers use case, however, it might help in any use case with lots of random writes such as iSCSI with several VMs.
- The faster 2.2GHz processor on the N54L can increase transfer speeds, but the 1.5GHz N40L can solidly get something like 55-60MB/s bulk serial transfers over CIFS to/from a 5x 3TB WD Red Z2 array (that's the only one we did significant bandwidth testing on so far, I would like to do more, but don't have a ton of time.)
- The N40L cannot handle 1080p Plex transcodes, but the N54L can - I don't run Plex, but I have heard that Plex server works great on a nVidia shield, which is probably easier to set up Plex on and has more transcoding headroom coupled with an N40L than an N54L on it's own anyway.
- I haven't tried to do anything with jails or the BHYVE hypervisor, but I hear everything still works great on the N40L/N54L