IMO you are intent in going for the more expensive architecture X79 rather than a Z77 build without a particular need and thus spending money on a type of build which costs more money for features you will not use.
I was hoping that you would respond by noting other more intensive hyper-threading type work which would benefit from such a chipset type build but you have not done that.
As for your reasons in buying a separate sound card they are flawed. The driver support for the Realtek audio chips are phenomenally good with very regular driver release. The Via HD chip option, on my Z77 board, is also exceptionally good and has given me absolutely no issues with any game. Remember that the sound chip is built on board and thus there is no harm in using it and many reasons to prefer it. You would save money and it would simply work. In fact there can be more issues with having a sound card and drivers than they can by using the onboard sound chip.
The rig you noted...
...is similar to what I came from...
E8500
4GB RAM
1GB GTX 460
Windows 7x64 HP
I did overclock the E8500 to 4GHz and I would have preferred my GPU to yours, I had a 4870 512mb prior to that. But this is now what I have gone to...
Z77 board
3570k running at 4.5Ghz
12GB DDR3 12800 memory @ 1600mhz
Asus GTX 670 Direct CU II 2GB
...the difference you would think would be great when playing games, I play them at 1080p, well it isn't.
The difference has not been "night and day" but more of an incremental one. Sure Civ V is now quicker between turns and when scrolling a larger map. Shogun II is likewise. Other games allow a little mor eeye candy. But they are only incremental differences and not in themselves enough of a justification to spend what I did to call it value for money. However there were other reasons as to why I changed my PC.
As noted I now have a 256GB SSD just for my Steam games and that does help, somewhat.
Unless you like playing with benchmark speeds you will not benefit at all with the faster RAM. The only reason that I have 12GB is that I did buy 2x4GB sticks of Corsair LP 1.35v memory and fitted that but then I "found" 2x2GB sticks of OCZ 1.35v memory that I had for a couple of years and forgotten all about it and thus I stuck that in as well.
I have noted absolutely no difference in game terms having come from 4GB of DDR2 to 12GB of DDR3. Sure it is nice for working with large raw images in Photoshop but we are talking about games here and in that context nothing has improved.
I still recommend a budget type Z77 board like the Gigabyte Z77 D3H (as this chipset will be the last for the socket 1155 and next year brings Haswell) I would not spend more.
As you do not wish to overclock at all I would then buy a 3570k rather than a SB 2500k.
I would also use the onboard sound and most certainly buy a GTX 670, non reference card - like the Gigabyte Windforce or my Asus one.
8GB of memory would be fine (leaving two slots free).
An SSD would be nice as a boot drive and another for the games. They would offer value for money.
Shogun II has been appallingly coded to take any advantage of a multicore CPU. Anything more than a single core at its very fastest is quite wasted and also damning of the creators considering the time we live in and the complexity of the game. So be wary in thinking that the entire solution lies in just throwing a lot of money into a hyper-threading system and that the TW games will take full advantage because they will not do that.
The system that you propose is a really good one and if you are only able to go for the X79 type build then it will suit you well. Shogun II should play fine but will not use the multi core or hyper-threading you have paid for. There are cheaper options which would be more suited to a gaming rig over the X79 chipset build you have listed. You also note that you will use a single screen and unless that is much over 1080p I see little point in going beyond that of a GTX670.
TLDR version - if you have to go with what you list...
Drop the sound card
8GB of memory will be fine
670 GTX over the 680
Buy a SSD for the boot drive (64GB)
Buy a Samsung Series 830 256GB SSD (for example) for your Steam folder
Have the 1TB mechanical HD you noted for odds and sods etc.
Hope the above helps and the best of luck
