once again everyone associates "controlling the living room" with xbox because a few MS guys said so.  Last I checked their console doesn't play blu-rays and charges for the apps you can use on PS3 for free.

3.5gb is already insane for games. It all depends on memory bandwidth anyway, doesn't matter how much memory you have, if you can't manipulate it fast enough it's all pointless.

It will be a while before the new machines will be fully used too. Optimizing games for 8 cores is not easy.

More RAm means that devs can cache more unique data meaning they can avoid loading from disc/HD. That can mean larger and more varied environments with more unique assets (NPCs, props etc) in an area for example. Less/shorter loading screens less stuttering in open world games etc. As well as more diverse interactivity and things like animation variety as more possible configurations can be cached.

Faster RAM allows more unique data to be actually used per frame so devs could utilise more data per frame. As long as devs use smart instancing and streaming they can have more detailed models etc on screen at once for example. There is not much point having 1000s of unique textures if you can only access a few for each frame after all.

But there are a lot of different factors for example if the X720 has a large pool of high bandwidth embedded memory for framebuffer and caching in addition to the main pool of RAM. But the PS4 has to use the one pool of RAM for everything including the very bandwidth intensive framebuffer, then the picture changes. Memory latency will also be a factor while GDDR5 may offer much higher bandwidth than DDR3 it also has a lot longer latency, which can effect certain tasks. That can be mitigated with large caches tho.

In other words it's really complicated and can't really be considered in isolation, you need a complete picture before knowing how it will shake down. Different games and engines will have different requirements and there are ways of designing around the different bottlenecks and taking advantage of each configuration. So even with a complete picture it will still vary from game to game which setup is actually better.

There are people on here that know more than me so they can correct me if I got anything wrong

thank you I realize there are still a lot of variables but just thought I'd ask anyway.

Depends on too many more details to answer. RAM speed, bus width, eDRAM, HDD and Disc Drive speeds and much more.

By themselves, Zarx covered them well but because computer, and consoles, are such complex devices that all depend on their interconnected components, you can't draw any conclusions on single knowns.