If you spend time waiting for the next generation of CPU to come out, you'll never upgrade lol.
Based on 30 years of personal computing history, Haswell is not going to be a re-invention of the wheel. At best (and I seriously doubt it), Haswell might be a 15% improvement over Ivy Bridge. But more realistically, 10%. Advances to hardware is done in baby steps, rarely huge leaps and bounds. 10%-15% is not really a noticeable difference in many things, but considering there is a HUGE difference between one of the best C2Ds and the 3770K, well.. you tell me.. what does your system do for you now that you think could be done better?
^ Well, next year, you'll be buying a new motherboard again in order to have a Haswell chip. From knowing you on the forums, it seems like you just recently got an i3 Ivy Bridge.. You should have just saved up for another month and gotten an i5-3450 or something in the first place.
If I'm running 2 GTX 670s in SLI, will the i7 3770k 3.5GHz be enough to handle it?
I'm playing GW2 atm and a lot of player's have reported that it's particularly cpu dependent and thus some of them are being bottlenecked by their cpus when running SLI.
Honestly, the only feature that i7s have that i5s don't is HyperThreading, no game uses it, and no future game likely will. Certainly if they do, by the time its a necessity, your i7-3770K will be a "dinosaur" just like the C2D. (Just to avoid arguments, yes I know the C2D is still a capable CPU for daily tasks, I have one in a laptop I still use- but anything older than 4 years by my working definition is a "dinosaur")
Having said that, you may consider looking at i5-3570Ks for gaming. Now if you're getting into heavy productivity work like video editing, CAD design, etc, then you might look at the i7s, but unless you're doing that kind of stuff professionally, even then the i5-3570K has plenty of power to do the job.
Programs must be designed to use HT. Simply running a lot of different programs at once does not mean HT will kick in. Actually Windows background programs will likely make use of HT to some degree if the 4 cores are busy with the programs you have loaded. Windows background programs generally do not take much processing power, so any such background programs using HT will have a negligible affect.
What about partially heavy mulit-tasking? I often run GW2 with GW 1 in the background (selling stuff), tabbing out to check the net, while watching a show on a second monitor...
My Phenom II can do that, not GW specifically, but I'm a heavy multi-tasker with a dual monitor setup as well, I've been known to play games while watching a movie, or browsing, etc. If my CPU can do it, an i5-3570K can certainly do it.