I'm running a Linux software RAID 5 (actually, two.) on my NAS, and it's plenty fast. Maybe Windows is a bit slower, but I wouldn't really recommend Windows for a NAS anyway.
There are some relatively easy to deploy NAS specific Linux and Unix distributions (the latter support ZFS, which can be nice to have).
Whatever you do, run a software solution, for price and fail-over reasons. Get a UPS as well, so the file system won't be corrupted.
Photography usually doesn't have such extreme storage requirements. I would go for a software RAID 5 as primary partition, a non-live but integrated backup (RAID 5, if you want make sure a rebuild from the backup won't fail because one disk fails out) and -- depending on the worth of what you're doing -- an off-site backup.
Full, spontaneous, unrecoverable drive failures are pretty rare these days, so a RAID 5 should be good enough from a reliability point of view, and it will keep you online and productive when a disk does drops. With regular surface scrubbing (checking for read errors, rebuilding the sector if there is one) you can maintain a high reliability FS. The backup will then be mostly for software or mis-manipulation issues.
Off-site adds protection against theft, fire or massive electrical damage. The last in particular is problematic, but can be reduced in probability by adding protection circuitry, or by physically unplugging the backup when it's not needed (hot swap bays aren't too expensive).
Oh, and use encryption, when you use RAID, so you don't have to worry about faulty drives leaking data, when you send them in for replacement, or eventually trash them.