You won't get much from an SSD unless you have Sata3. They are faster, but you will only see half the gain without Sata3.
I would pass on the older 6 core AMD, it isn't much faster than first Gen I5 or even an older Q9550 (seriously), not that impressive in my opinion, at least compared to a newer I5's and I7. Intel had and still holds a massive performance lead. If I was to go AMD though, it would be the newer FM2 Trinity series. I built one the other day (A10 5800k) and I was extremely impressed and I wouldn't get anything less than that. It's decently fast, but as tp4tissue mentioned, an overclocked I5 will still destroy it. On the other hand, keep in mind that either of these have more than enough power and will make your q6600 look pathetic.
I definitely agree with Badwrench on memory. I have 16gigs and 8 of it is pretty much wasted.
Also, buying 16gigs of DDR2, have you looked at the price for that? When I wanted 16gigs of it, it was cheaper to buy a new board, DDR3 and a new I5! Even used, it likely won't be cheap by any means. Besides that, most DDR2 boards won't support 16gigs. Not that you need it.
By switching to something newer, you not only get DDR3, you also get Sata3 and USB 3. Not a bad deal.
Raid... If you can avoid it, do.
It's at least twice as likely to fail. 2 drives, each with a chance of failure, plus you can have software/hardware failure as well. On newer SSD's they flow enough data to where it doesn't matter anyhow (on Satat3).
I would encourage you to consider your backup system as well since you plan to have so much storage, particularly raid storage. That much storage, when full, is a backup nightmare. One thing I did was I made a deal with someone to host a small system at their office. In exchange for that, I backup their office to my house, my house to the office. I made a full backup over local network before moving the system.
