FWIW, I have seen dual drive failures of Hitachi's 15K300 drives in fairly close succession. At home with more normal discs, I've seen enough failures that I wish I'd bought a RAID6 capable card.
One contributing factor is you say you've got 6 2TB Samsung drives. That presumably means you bought them at the same time from the same shop, and so they are very likely all the same manufacturing batch - that increases the change of them failing together. I've had 4 drive failures, of which 3 were a set of discs I bought at the same time and they have almost sequential serial numbers, and failed weeks apart from each other.
I'd definitely pick the RAID6 solution. However be aware that it only protects you from drive failures. A friend of mine went to a lot of effort with RAID, only to see a power spike wipe out the whole PC.