Tusker 21,
You've just given a new meaning to 'reliability'. Is this the new 'Jubilee' dictionary? My understanding of reliable is quite different, but that depends either on my memory (could be corrupt registers problem) or the dictionary.
What you have given is a requirement and from what I gather RAID levels are different and geared to achieve different factors. So you may be looking at RAID5 or RAID10 (or maybe RAID6 - if the device you ultimately go for supports it).
For you, it's now important to look into that as the determinant for the device you are gonna buy.
I have not tried any NASes with SSD. You must be having a good budget, right? SSDs still don't come cheap!
At the moment I have some D-Link NASes (DNS-343 and DNS-323). The problem I've had with 323 is that it kinda disconnects sessions whenever I change a user's credentials - like network access or even passwords. I haven't had that with 343. The 343 is 4-bay (4 disks) while 323 is 2-bay. You should be looking at the 343 on the least.
I don't know your environment but DNS-1550-04 will probably sort you out because it has almost all RAID levels and takes many disks. Problem is whether they are available locally. I think Coast Data has 343.... not sure about the others.
Did you look at the Synology range yet?