Quick answers to your questions. You can definitely configure unRaid to saturate your gigabit lan. Either with a cache disk, or using turbo write.
Most of the functions you want are available in Dockers, which are very easy to install and use. @Squid's excellent community applications plugin should be one of the first things installed.
Can't speak to comparisons with other products. Do your homework and make your choices. Most people here are pretty happy with unRaid, and we do have a friendly community. @Lev's split personality response above is not altogether typical
But unRaid isn't always push a button and its done. It is largely dependent on other products and their feature sets for things like backups. And your ingenuity in getting them configured and integrated. OOTB function is easy, but your know-how, trial and error, write-ups/videos from other users, and pointers from the community will very likely get you to workable solutions.
If you decide to move to unRaid, I'd initially focus on establishing the parity protected array, and getting your existing features replicated in unRaid. Optimally you would set up a second / temporary server to experiment and get things working, and then plan a conversion from FreeNas. It doesn't have to be very powerful. But all unRaid needs is a USB stick to boot, so you could probably boot unRaid on your current server and experiment, and then boot back into Freenss, until the transformation is complete. Just make sure not to reuse assets, like your current drives, for unRaid!
Good luck!