If you recall back when Netburst was new, Intel used the same socket for laptop, desktop and server = mPGA478. Over the years and architectures, Intel realized each market has their own needs, so multiple sockets came (not like that couldn't afford it
). Midrange desktop on down stayed in what Intel calls their mainstream client socket (LGA775) and it's successors (LGA115x), but high-end desktop moved into one of Intel's many server sockets and that's where that market stayed with LGA1366 and LGA2011. They don't overlap or mix'n match, or represent each other.
I think what bugs people most is that these chipsets and sockets are all on different schedules of succession, so the simplified straight-line thinking of yesteryears "newer is always better" doesn't apply anymore. This is because of AMD; for instance, Intel broke tradition of introducing high-end first beginig with Sandy Bridge because AMD could only afford to go after P55, thus Intel brought Sandy Bridge as P67 first instead of X79 first. AMD never bothered to make a competitor to X58 and so far haven't with X79. If anything, P67 was pre-emptive, and they over-estimated the impact of the very late AMD Bulldozer, we all did. So while Bulldozer's successor is a few months away, Intel pre-empts again with Ivy Bridge (Z77) which will no doubt win again.
We could conclude Intel moving high-end to another socket was a pre-emptive move against AMD's first quad-core and what it could do, but that would imply a lot more than rumors avilable even at the time; especially since the first Phenom quad performed like a Core 2 Quad. It was my theory at the time, but few agreed with me.
Anyway, back to your question regarding PCIe 3.0 and new cards,
this recent review of the latest GTX680 and HD7970 shows they don't loose much more than 25% performance even if put a PCIe 1.1 x16 slot, which is what you have in your 680i. Considering you had only one 8800GTX this whle time, what are the chances you only 1-2 graphics cards versus more? That is what separates the sockets; Intel made X58 and X79 for access to 6-core processors and enough PCIe lanes for more than two graphics cards. If only intending 1-2 graphics cards, you can stay with LGA1155.
Just so you know, despite quads been around for six years, most games are still coded for 2-4 cores because most folks still get only those processors, so don't get a 6-core for gaming unless you intend to keep it for as long as you had your E6850. Games take a few years to make from the ground-up, so it would be a gamble. 6-cores are meant for more than gaming, like photo or video editting and encoding, etc.
But you want something simple, I recommend a Z77 board with a single GTX680 and Core i 3000 series part. Just so you know, Intel killed the freedom to pick any CPU and overclock with Sandy Bridge. Now all new processors are limited and those with letter K are flexible, popular and expensive. Also, since Nehalem in 2008/2009, Intel included a new kind of hyperthreating, which has a hit/miss performance improvement, usualy 5%, and some games don't like it. So I suggest the 3570K w/o HT and the K for overclocking if you intend to someday. As for PSU, get a 500W unit with at least 35A on 12v if you aren't overclocking, add 50% if you do intend with a second GTX680 someday.
Just so you know, Intel wil pushing another new architecture by spring next year, in a new socket set, LGA1150 will succeed LGA1155, so of course processors won't mix and match. If you can wait 8 months, it would be good for you. If not, it doesn't matter what you get, even if AMD; they're all faster than a Core 2 Duo with a 8800GTX. By next year, both AMD and Intel's integrated video will get very close to your 8800GTX for comparison, so you've waited long enough, IMO.
Also, your resolution isn't out-of-date, unless you want more.