For your hard drive edit: Seagate = no! For whatever inexplicable reason, Seagate drives have seen a higher failure rate since the introduction of the 7200.11 drives, which were also louder than previous generations; this has been going on for years. Newegg is a great source of reliability trends for these sorts of things, and will very quickly show you what I mean. The recommendation is to stick to WD first, and Samsung second, for secondary storage needs.
I'll echo the vote for the Spinpoint (or WD Green). The WD Black is the fastest (and by informal vote the most reliable of the faster drives), but it's also the hottest and by far the loudest- it's seek noise is downright harsh. The Samsung is nearly as fast and comes with a shorter warranty (3 years to the Black's 5 years), but it's definitely cooler and quieter, and the seek noise while still more than audible is muted in character. The Green drive (bear with me!) is quieter than either during seek, also with a muted character, and is even cooler.
I have used all three of these drives in personal systems, and if I were in your situation with an SSD, it would be a vote of Samsung for secondary speed or the WD Green for overall system noise, and would hinge on whether or not you feel that you could comfortably fit the files and applications on the SSD. If you can get applications and most used games on there, keep in mind that you can use Symlinks to move things around as needed, then I'd recommend the Green, but if you feel that you will be running performance sensitive applications or storing files such as Photoshop/Premiere workspaces on the mechanical, then I'd recommend the Samsung.
Personally, I steer towards silence after my performance considerations have been met, and my wish list includes only an SSD and WD Green drives for that reason. Moving on:
'V3' on the motherboard would seem to indicate the 'B3' stepping for the fixed P67 chipset.
Make sure that those XFX Radeons use the stock HSF or similar design that intakes as far into the case as possible and exhausts only through the slots and out of the case, as otherwise the top card's intake will be inhibited by the bottom card.
You're building a gaming build, so consider Auzentech's wares if available; their Forte', while more expensive, provides full hardware acceleration along with all the usual X-Fi features, and a decent headphone amp as well. No complaints on Asus' Xonars though. Also consider Creative's new (Titanium something?) card, if you'd like. After years of crabs, for which I have nothing but praise for given their price, the idea of software sound and dropped voices/sounds in games is starting to get to me.
For the 1155 vs. 1156 compatibility concern- don't be, they're the same dimension.
For the H70- consider either the Antec mentioned above, or Corsair's forthcoming H60, if available. Both the H50 and H70 are very effective coolers, but they're also marginally louder than they need to be, and more expensive than air coolers which cost less and produce less noise, and have a lower potential for failure without the pump and tubing. The other watercoolers mentioned (Antec and H60) are both quieter than Corsair's first forays and worth the price, in my opinion.
Further note on the self-contained water coolers- these are designed to be installed as intakes, not exhausts. Your selected Corsair case appears to be set up for bottom to top airflow, with a negative pressure setup (more exhaust than intake), so this configuration would seem to work well for you; the radiator and fan would be mounted on the rear 120mm fan mount, and the air it pulls in would be immediately exhausted by the top three fans, by my observation.
Your PSU is exactly the unit I would specify for your build, with the exception added that if either an HX850 or AX750 or AX850 were to be available for a small additional investment, I'd probably make the jump.
Let us know what you think and if you have any further questions!
Canon 6D|24-105/4L IS USM|70-300/4-5.6 IS USM|40/2.8 STM|50/1.4 USM|85/1.8 USM|Samyang/Bower 14/2.8 Full-Manual Rectilinear Wide-angle|24/2.8 IS USM|
Canon EOS-M|11-22/4-5.6 IS STM|22/2 STM|EF-M 18-55/3.5-5.6 IS STM|