It's not about performance, it's about data security by instantaneous backup (hence RAID 1).
I'm not a commercial organisation with critical data, I don't need gold-standard backup procedures, and life gets in the way of routine housekeeping... so defending against HDD failure using a mirror drive seems like the way to go for me.
Back in IDE days I had an AMD486 motherboard which did hardware RAID and even fooled Windows into thinking it was just a disk. I was very disappointed when I discovered my current mobo RAID support is essentially through drivers, so I ditched that idea and got to grips with mdadm. Any hardware RAID adapter cards I could find looked expensive, but I'm happy to follow up your suggestion.
If I can put the RAID at the hardware level, that's one less thing for the OS to get in the way of, but something to ponder: from what I've seen so far, the RAID drives under mdadm are pretty safe from a raw Mint installation without mdadm installed, and then installing mdadm makes the existing RAID drives available again. That seems pretty robust. If the hardware RAID card failed, it would have to be replaced.
A nice feature of the AMD486 hardware RAID was that each drive was just "normal" - if the PC went dead, either drive would work directly on another PC without special measures. Is that the same with your 6805T?
Update: £24 + delivery, that's OK. If I saw it before I would have not understood "SAS".
Note to self: http://download.adaptec.com/pdfs/user_g ... 2_2011.pdf