You'll notice that P&R as well as the "spam" sections arguably have higher activity, but these hardware forums do get activity. Just a bit slower for a response.
Couple things to touch on- the jump to an i7 likely wont be night and day unless you do specific tasks that'll benefit from a beefier CPU. But you will see an improvement across the board and I'm certain it'll be noticeable. How noticeable, again that depends on usage but it will be noticeable.
As to the GPU- any mainstream or higher GPU out right now will play every game available. My 5870 allows me to max all in-game settings in every game @ 1920 x 1200. I do however have to drop the AA or do without AA in certain titles.
Right now nVidia only has one card of the 6 series out and that is the GTX680. It is a good card no doubt, but most will agree that it is considerably over priced. And it's performance compared to the GTX580/570/560 isn't that much of a leap. It is an improvement but really not worthy of the GTX680 name. It performs more like a GTX670 imo. Maybe even GTX660Ti. But it is what it is.
I'd imagine at your resolution a 680 would allow you to play every game out there, maxed in game visuals, with 4xAA rather comfortably. You may have to accept some slow downs on the rare occassion but I doubt it'd be often.
As for AMD, well they have the 7970 as their flag ship and have released the better part of their 7-series line up. You have the 7750 up through the 7970. Considering the resolution you're playing at as well as your desire to use AA I'd suggest no less than a 7950 from AMD. 7970 if you can spare the cash.
But just like the GTX680 most will agree that the 7-series from AMD is over priced presently as well.
If you want my honest opinion I'd go through the the CPU upgrade first and rock that 6870 for a while longer. There are several possibilities as to what can happen in the future regarding video cards but one thing I'm certain of is you will see prices drop in the coming months. No hard evidence to back that up, just basic common sense. As nVidia releases more of their 6 series putting pressure on AMD, AMD will have to respond with lower prices. Since AMD responds with lower prices, nVidia will have to follow suit as well.
Me? I'd love to get a new video card but just don't see any out that would warrant the upgrade cost. I'm waiting. Not sure for how long but I'm in no hurry as I'm very pleased with this 5870. I am eyeing the 7870s right now but they're just not priced right IMO. If they don't drop to a reasonable price soon I may wait till the end of this year when AMD is rumored to release it's HD8k series. But again, I'm in no hurry. Waiting that long may not be advisable for you.