It needs to be considered what multitasking means to different people. In Lambe's case, they mentioned gaming while having browser tabs open. Obviously you're either actively browsing the web or playing a game, not both. No one can unless there's a dual mouse setup I'm unaware of. In this case, it means more ram will be beneficial, the cpu will only be running the game or the browser and a browser takes up very little cpu. Even if there are multiple webpages loading, this will depend more on the internet connection speed downloading in the background and if downloading to the same hard drive (or ssd) as the game is being played from that will be the bottleneck in i/o transfers.
Most people who do even frequent streaming think it's all about the cpu and there's more to it. Unfortunately there's never a simple solution to anything such as 'just this' or 'just that'. Those serious about streaming and who want quality streams use a second system. Again there are storage and memory system issues that can crop up and affect the quality of a stream using a single system with multiple cores.
It also depends on the software used, some software imposes higher load on the cpu than others. Shadowplay with nvidia cards works really well and offloads most of the work to the gpu so there's little performance hit to the cpu. We already know there are some games that are cpu heavy and others that are gpu heavy so it's not accurate to simply say a 'gaming' pc. One has to consider which games. Same goes for other software as well.
More cores isn't always the answer, obviously or the fx series wouldn't be so easily outperformed by intel's i5's and i7's which are just quad core cpus. A quad core without hyperthreading (4c/4t) system may lag a little while live streaming but an fx 8350 will perform less in just about all games. In terms of streaming using obs to twitch, the i5 has a lot less frame drops than the fx 8350.
https://www.youtube.com/watch?v=26UKz42uQ1Y
If more cores were better, ps4 and xbox would be better than even budget g3258/i3/fx 4xxx/athlon x4 860k. It's pretty evident this isn't the case, more weaker cores don't equate to better performance. This was pretty quickly made clear when amd hyped their 8 core bulldozer chips and they decided 'moar' was better. They convinced people this was the case and it's not true. In very few cases are more weaker cores better. It's not that I'm a particular fan of either, I'm a fan of performance. If amd had it I'd buy it and have no issue recommending it. It would be ridiculous to buy intel if it performed worse and vice versa.
This isn't necessarily a 'benchmark', just a user's experience where performance even while streaming went up switching to an i5 over an 8350. It basically coincides with what was found in the results from techyescity's review.
http://www.reddit.com/r/pcmasterrace/comments/2r9opt/will_an_i5_4690k_be_enough_for_daily_streaming/
A similar experience on an xsplit forum.
https://support.xsplit.com/forum/viewtopic.php?t=16871