@michael123 how that's a GREAT question. I've tried both unRaid and FreeNAS, but wow it's not a easy and quick way to answer.
All those things you mention is why I love unRaid. I've used it for many years so I'm very comfortable in knowing how it works, how to perform many advanced tasks both in the GUI and the command line and where it's limits are defined. I think it's in this simplicity that it's so adaptable. Hrmm, see I just typed all that and really said nothing to answer your question. I knew this would be tough question.
unRAID is fantastic, it works exactly as where the expectations have been set. I don't like when others call certain functions of it 'slow' because really it's 'working as designed', slow/fast is subjective opinion. Does it meet the design and communicated features, yes unRAID does. However there are ways, unsupported of course, to improve functions:
Parity checks, or writing to a parity protected array. How to make it go faster? There are ways.
How to write to multiple UserShares in parallel and achieve full disk I/O on a 10GB network? There are ways.
Creating a single parity disk in RAID10 that will statistically will never fail? There are ways.
I've been tinkering a lot of my Areca RAID adapters when it comes to Parity, Cache and Unassigned Devices drives. For my data drives I use the normal LSI 23XX HBA cards. RAID just enhances those select areas, which I think enhance the essence of what unRAID is. It's not supported, not for everyone, but if you got the time and money, which looks like you do, then spice it up.