Nanofrog: budget is around $6.5-7k. Already have my 30 dell, and my 4x2 gigs HDD that I've taken out from my "old" rig.
So basically what I'm looking at is:
-Ram
-Intel 320 series 160gig boot drive
-6 or 12 core MP
Cannibalizing gear from your previous system is always nice.

Especially large screen monitors, as those can set you back quite a bit (Eizo's 30" ColorEdge series comes to mind at over $5k USD;
example).
But I'm curious as to what you plan to do for storage.

The SSD will make a wonderful OS/applications disk,
but what do you plan to do with the 4x 2TB disks?
I ask, as though a stripe set can offer raw speed, it's not even as reliable as a single disk. This is fine for a hobbyist that can afford the time necessary to fix it when it breaks (replace the bad disk, restore from backups, and re-perform any lost work that occurred between the last backup and when the array failed), but not so much for professionals, where time literally does = money.
As it happens, the MP can also do level
10 (0/1/10 and JBOD to be thorough), which will offer you some redundancy. But it comes at a speed and capacity penalty that may not be viable (4TB usable capacity with your existing 4x 2TB disks), and you're still missing a backup solution.
A hardware RAID, such as RAID 5 may be in order, but it's not exactly inexpensive either, as you'll need a controller, enterprise disks, and some additional hardware (either an internal mounting kit, external enclosure, or both). I'd need specifics to go any further, but it offers a great balance of performance and capacity (not quite as fast as a stripe set for the same number of disks, but it's redundant).
Something you need to think about carefully (i.e. SP Hex + storage system that can keep the cores fed vs. more cores <12 in particular> that will be starved because the storage system cannot remotely keep up).
So I'd figure out the storage solution (+ any other upgrades you may still need, such as memory), deduct that from your budget, and that will dictate which machine will be possible. I suspect the SP Hex (really nice machine for the money, as it's faster for both single and multi-threaded applications than the current Octad for just a couple of hundred more), but this is more out of an educated guess as to what you'd really need for storage (based on a presumption of a
busy professional editor).
In fact, the storage + memory + SP Hex could exceed your budget.

Seriously. But it will depend on your specific needs (immediate capacity and future growth + performance to dictate the number of ports for the card, member count <disks>, and additional hardware to connect it all together).
What I would really like to avoid is to spend a huge amount of money on something that _might_ get bumped thus making my investment somewhat obsolete ( when talking about possible resale value later on).
As a professional, resale value shouldn't be a concern as the machine will pay for itself multiple times over if you have the business and do it right (get the right machine + upgrades).
Now as to trying to plan for the future, that's difficult on a good day (not impossible to do, but things change rapidly and can destroy the best laid plans, such as expecting say 4TB capacity growth per year, but end up with 2x or more of that figure). If all goes well however (increased income generated), such a situation wouldn't be that difficult to work out (just buy more disks and enclosures, maybe a larger RAID card or additional card if necessary).
In terms of software, you could wait until more information comes out on FCP X as it's not that far off from what I'm reading. Past that, I'd recommend considering anything else not announced vaporware (don't make assumptions as to what features are coming <next week, according to
this>, let alone when as you've an immediate need).
We're not even sure TB will be successful. Adoption outside of Apple is at a snail's pace. Even Apple's own lineup doesn't entirely include it. Sony has already "fragmented" TB by including it, but using a different connector. The statement that PCIe cards will not be available for existing computers is a kick in the nuts. Video card makers are annoyed that TB actually has much less bandwidth than display port 1.2, thus preventing monitor daisy chaining from the TB/DP connector.
I like Thunderbolt a lot, but there are problems to overcome including USB 3.0 which got a good head start and is backwards compatible with about everything made under the sun.
There's a
front page article that might be of interest.

Assuming this actually comes to fruition (in terms of the peripherals, presuming they're not sold with an Apple label on them), it could ramp up the adoption rate for TB.