People get too lost in buzzwords and sales gibberish.
Loads of games like to say optimised for multicore, because it sounds like you're getting more for your money, like they've made an effort to make the game more complex to use a quad core.
99% of the games that are optimised for quad core, will just use a 25% load on 4 cores, instead of a 50% load on 2 cores, or 100% on one core. THeres a difference between being ABLE to use multiple threads(which is incredibly easy) and NEEDING to use multiple threads. Its easy to use multiple threads as there were always multiple threads essentially, packaged into one easy to use .exe that did them all in one go.
Separate sound, physics, ai, gfx driver and a few other things into separate threads and its easy to push a little of the load across cores, spliting a single thread, like the main game engine across more threads is more difficult but more and more doable.
Theres no need, especially for gaming, for anything other than a midrange quad core.
Its very hard to predict exact performance. Core 2 architecture in general was a 4 issue interger core, that uses hyperthreading to "fill up" the 4 issues each clock because most threads don't use all 4 issues, the few that do, like Superpi, are usually incredibly basic so not that representative of real world performance.
Phenom is a 3 issue core, but apparently rarely uses all 3 well, Bulldozer is moving to a 2 issue core, but a much more streamlined and inteligent 2 issue core with vastly better thread prediction, their 2 issue core should be noticeably faster on a single thread(the vast majority of them) than the older 3 issue core but will it match best case scenario of the Intel 4 issue core, probably not. However across the "two cores" in a module you have essential 2x 2 issue cores, but that are always available. Multithreading it should honestly spank Sandybridge at similar prices, single threads are almost certainly going to depend on the thread. I'd expect something like Superpi to not improve, but more real world loads to get MUCH closer to Sandybridge than Phenom 2 is.
How much, who knows, it will vary depending on what kind of application most likely.
Technology wise its very interesting, its will be a leap forwards, not least because of the design, they've pushed a 8 core die into the space of an old 4 core die(give or take). Meaning they can sell an 8 core chip at the same cost as a current 4 core chip. Thats a huge improvement right there in terms of what the customer gets for their money.
But to be honest, and I've said this for a year, while Bulldozer was worth waiting for over upgrading in the past year, and a huge step forward, its ultimately a "fusion" design, just lacking the fusion part till gen 2. As Intel/AMD push gpu's on die AND push things like open cl and gpu acceleration of more and more "normal" cpu workload and more applications get acceleration, gpu on die will be the massive breakthrough in performance.
Bulldozer is set to be a great core as is, but with the IGP a year or so later, it could be epic.
so I may live on a very old AM2 system until this is out