Multiple cores = better multitasking?

Multiple cores = better multitasking?

Specifically I am looking at either the i5-3570k or the FX-8350, but it
made me think of a more general specific question on how multiple cores
can improve general multitasking.
Been reading a lot of reviews, benchmarks, etc, all basically say the same
thing: The faster clocked 4core I5 beats the slower clocked 8core FX in
most applications, unless that application is specifically coded to take
advantage of more then 4 cores. Games especially run better on the i5.
But as I was reading I noticed that pretty much all benchmarks are done in
a vacuum. That is, that benchmark or software is the only thing being
tested. But while that is good for testing that specific software, it's
hardly a real world scenario.
For example, at any point during the day I may have several browsers open
with several tabs, maybe Photoshop or Visual Studio, several background
programs (antivirus, steam, keepass, etc). And that's on a light day.
So my question is: Theoretically, while the faster 4core will run
individual pieces of software faster on their own, couldn't an 8core
processor be better at running multiple pieces of software, even if they
aren't necessarily 8core optimized, simultaneously?