If the system is for gaming, 16 gb is overkill. 4gb is enough for all games in existence now and in the near future. 8gb will last a long time, and is the usual amount of RAM for a game system on that budget.
An 850w PSU is complete and utter overkill for a single GPU rig. Your system as built will barely draw 300w under full load. A 550w PSU will give you plenty of overhead.
A 90gb ssd will only hold a few games in addition to the OS. I'd reccommend a 120-128gb drive. A Toggle-NAND, second gen sandforce drive will be faster than that drive, and about the same price (Sandisk extreme is my personal preference). A samsung 830 is a great choice as well, though it's slightly more expensive.
I'd use the money you save on the PSU and RAM to bump the video card up to a gtx 670 or HD 7950.
If you just want to shave a little cost 8GB is plenty these days.
If you're not going to SLI maybe drop down to a 550-600W PSU.
Do you really need a BR burner? External storage is cheap, you can install Windows from a USB stick, and very very few games are not available as digital downloads. Discs are headed the way of the floppy rapidly. (truth in advertising - I bought a DVD burner for this new build for $25 since I was too skeered not to - but don't think it has a lot of value).
Pairing a pretty high end mobo with a mainstream CPU and GPU. Could drop down to a LK or LX version and save a bit of money and still overclock.
Right, it's more expensive but that's because it's a better PSU. Look at Seasonic, XFX, Corsair, and PC Power and Cooling for solid PSUs. Here's a 650W from Corsair that is a bit cheaper and will 100% run your system as is with no power issues.
Hard to tell. I can't find any reviews on the product, and there are only a few reviewers on Newegg. I'd go with a brand that has more history in the SSD market, like one of the ones I linked, or maybe a Crucial M4, though their 128GB has been a bit more expensive the last month or so (around $110 compared to around $100) than OCZ or Samsung 830s.
I agree with all these recommendations, here are a couple more thoughts.
I have 16GB of ram in my system because it's future-proof and ram is not very expensive these days. 16GB may be overkill today, however this system should last for YEARS so I believe 16GB is a sound investment if you aren't paying over 200 bucks to get it.
Don't waste your SSD by putting games on it. The caviar black gives excellent performance and with the OS and virtual memory being on the SSD, I find you can put your games on the caviar and it runs great. Thus, you don't need a big SSD, just a very high performing one.
You have to be very careful when installing windows - it will spread its partitions randomly over your multiple drives, so only have the SSD connected when you install windows, so that every aspect of the OS ends up on the SSD. Once windows is fully up and running, then connect your caviar.
It's good to see you are avoiding OCZ, apparently their reliability is poor. Seriously.
Good choice: Go Nvidia for the video card. ATI cards do not perform as their average FPS benchmarks suggest. Period. For the past 15 years, very chance I took on an ATI card resulted in disappointing performance compared to the benchmark, over and over and over again.
All and all the choice of parts is exactly what you want - no more and no less. Intel, Nvidia, and Corsair FTW. No need for an i7, no need for > 650GTX,
.. and Btw, no need for Windows 8. Score Win7 while you still can.