ok so lets straighten all of this out for you....
Currently you have a Sandy Bridge CPU, a LGA 1155 socket, and a motherboard with a 1155 socket and a PCIe 3.0 x16 capable slot. Technically, right now that slot is really PCIe 2.1 x16 or PCIe 2.0 x16. The slot can become a PCIe 3.0 x16 if you update the BIOS/motherboard firmware and have a CPU that is a 1155 socket and has a PCIe 3.0 controller.
As of right now, Sandy Bridge-E(Extreme) CPUs are the only CPUs with a PCIe 3.0 controller, but are a 2011 socket and are $600-$1000. Since they have a different socket, they need a different motherboard with a 2011 socket, not a 1155.
This means in order for you to get full use of PCIe 3.0 you need a new motherboard, a PCIe 3.0 GPU, and a new CPU, OR you can wait for Ivy Bridge to come out and just buy a new CPU. As stated before Ivy Bridge is going to be about the same prices as Sandy Bridge CPUs. Sandy Bridge-E in this case and purposes is totally separate from plain old regular Sandy Bridge CPUs.
Now how does PCIe 3.0 compare to PCIe 2.0 with current GPUs...
http://www.hardwarecanucks.com/forum/hardware-canucks-reviews/49646-amd-radeon-hd-7970-3gb-review-21.html
Basically not much of a difference...
Now Intel's CPU structure...
They do a tick-tock method as they call it. A tock is a new microarchitecture and a tick is a die shrink. Ivy Bridge is a tick so it is a die shrink which for this case is the transistors in the chip going from 32nm to 22nm in size (Sandy Bridge has 32nm transistors). Haswell will be a tock so it will have a new microarchitecture so in lame mans terms will have a new socket, the 1150. Ticks big thing is using less energy/power and tocks big thing is increase in performance. The thought being for DESKTOP CPUs, Sandy Bridge is 3.2GHz, 4 cores @ 95watts and Ivy Bridge is 3.3GHz, 4 cores @ 77watts and Haswell will be 3.3+GHz(easily), 4 cores @ ~77watts(nothing is truly known for Haswell except it doesnt look to have more than 4 cores partially thanks to E/Extreme Series CPUs(thats a whole other topic)). Haswell is Q1 of 2013 still though and again a LOT is still unknown.
With that being said...it is probably not in your best interest to upgrade CPUs even for Ivy Bridge. Your Sandy bridge will be doing about only ~15% less than the equivalent Ivy Bridge CPU and running at a few more watts. Nothing too big of a deal. I think you should be able to get 4yrs out of Sandy Bridge with like a GPU update if needed in like 2 years. That's pretty standard in my opinion for PCs and means you've gotten pretty good use out of it. And in 4 years it will probably be time with new RAM taking over the market, USB 3.0 in full throttle, and thunderbolts up-coming with of course even better CPUs.