I moved my big ZFS array from a working OpenSolaris system to ZFS on Linux!
Previously I was running Linux but on a VirtualBox hosted by OpenSolaris, mounting ZFS over NFS, which turns out to be very slow (VirtualBox seems kind of slow at network I/O. KVM is the more modern way to do this, and I suspect it's a better way.)
I would guess that the Linux port of ZFS is somewhat slower, but it's totally great to have all my stuff on Linux again, and for certain, the apps I'm running on Linux are quite a bit faster now.
This new machine is the gen8 microserver, which in practice is quite a bit faster than my old 3GHz Xeon. I'm booting it to an ext4 SSD software RAID-1 (md), and then using the same LSI card that came with my Sans Digital TR8x for the external ZFS array.
Other than thinking "if it works don't fix it", the only thing that held me back from this move was the idea that NFSv4 ACLs (i.e. NTFS ACLs you copied from Windows to ZFS) would somehow make for a trainwreck when I moved away from the built-in Solaris CIFS service to Samba. I felt "locked in" somehow by setting up all those ACL bits. But no such catastrophe has occurred - a few chown's and an occasional setfacl and it's fine. The ACLs are inherited in ZFS (and there's a Samba option for this too), so most of it just continues to work.
Samba is probably faster too, because it supports SMB2 and CIFS does not. Also, if the ACL issue bugs you, you can even compile Samba with ZFS-style ACLs - I didn't even do this.
A Solaris-like auto-snapshot service is available with one git checkout: https://github.com/zfsonlinux/zfs-auto-snapshot. Everything else I was running is tons easier to configure on Linux anyway.
Maintaining one server OS is going to save me a lot of time, and for that alone, it was worth the move.