http://www.playstationlifestyle.net/2013/08/05/the-ps4s-big-challenge-is-its-amd-chip-that-heavily-relies-on-multi-threading-says-planetside-2-dev/
Quote from the above article:
As it says, the primary gameplay process/thread usually is heftier to calculate than lesser processes involved. I'm not completely sure what parts can and can't be parallellized as I'm no programmer, but I would guess that sound effects, logistics and physics can be separated into their own processes
to some degree, but because they all interact and require information from each other, you can't just split them into smaller processes. Programming in parallel is difficult to comprehend for anything other than "simple" embarrassingly parallel workloads, which sort of make sense even visualized in layman's terms (like multiple threads rendering equally big parts of an image..)
I don't think you're running into memory bandwidth issues though, I mean, look at Minecraft, it's relatively simple as a game but has to handle volumes of voxel data and freezes on the mightiest machine if you spawn too much TNT and make it explode.
But yeah, DDR2 and DDR3 didn't really make a big difference, neither will DDR4 as the other components (and programming, as noted here) lag way behind in an enormous majority of cases.
