Am I close to the edge...powerwise?

Hey guys, need some expert advice. I'd just swapped my 3rd rig from a Sharkoon T28 case to an NZXT Phantom 410 case. I don't know what possessed me, but I was too lazy to take out my SilverStone Op1000 PSU, and since I have a Seasonic SS-850AT Bronze lying around, I decided to go with it since it had a longer CPU power cable which would make it easier for me to route it thru the back. This is my PSU-
http://techshop.in/store/product_info.php?products_id=6957

Anyway, when all is done, it suddenly occurred to me that I may be pushing the PSU too much with my recent upgrades. Here's the full system spec-
C2Q X9650 @3.7ghz
Asus Maximus II Formula
2x 2GB KHX DDR2 PC8500
Sapphire HD6990 + MSI HD6970 Ligthning
1.5TB WDC Green
1TB Hitachi Deskstar
1x BR ROM Combo drive
1x DVD RW drive
1x red LED Strip/light
4x 120mm cae fans (intend to get 3 more for better airflow)
64bit Win7 HP

Other than the fans, I do not believe I'd be doing anymore upgrades to this rig. So, is the Seasonic SS-850AT enough?

If you don't OC the GPUs, yes.
The GPUs alone have a combined TDP of 625w. The CPU is 130w TDP stock (it may well not eat that much, though), OC'd figure 160w if the 130w is true. That's 785w. Add in a couple HDDs at 10w each, a few fans at 1w each, maybe 35w for mobo+RAM, and your PSU's 840w 12V rating is being brutalized a bit.

Now the odds of all that being at 100% load at the same time are mighty slim, it's rare that SLI/CFX pegs all cores at 100% with the CPU at the same. I think it unlikely that your PSU will explode, but it is definitely operating pretty close to the limit

The silverstone has a chunkier 960w 12V rating, but a smaller fan and lower efficiency. It may be a bit noisy at full blast!

I'd recommend swapping the Silverstone in despite the fact that I expect the seasonic to survive, or spending a bit of time/money in the classifieds picking up a 1kw PSU of the 80+ bronze or better sort.
The penalty for an overloaded PSU death can be high.

From what I can find online, yea you're pretty close with those (technically 3) GPU's. You should be pushing at least 750w with that setup at full tilt. Since the PSU is a Seasonic, it should be capable of 850W and then some, but I think I"d go back to your 1000W and get some cable extensions.

I've downclocked the Lightning from 940mhz to 830mhz (same as each core of my HD6990), hopefully, I'd save a little power from this. I have decided to add a 120mm non-LED fan to the front, and a 140mm LED fan on top to help with cooling. Meanwhile, I'm going to check on the rails from time to time and do my mental masturbation thing......would prolly get a new 1kW PSU to ease my mind. Sort of like what I'd done when I was running 3x HD7970 + 3960X rig with the HX1050....after a couple of nerve wrecking weeks, went for an X-1250.

OK, guys, a brief update.....I did as you guys had suggested and swapped out the Seasonic PSU for the OP1000. The Seasonic 850W PSU was really struggling with the added load of the 2nd card. I'd even gotten a system reboot when I was halfway done with a benchmark, but when it rebooted, it automatically disabled CF (I didn't know the system was 'intelligent' enough to do that).

Anyway, with the OP1000 installed, everything seems to be running fine. I had even managed a few benchmark runs without issue.....thanks for the great advice guys!

Edit - Here's a pic of the OP1000 back where it belongs...