In the words of the great John Carmack:
http://www.ign.com/articles/2013/08/02/carmack-says-xbox-one-and-ps4-hardware-essentially-the-same
I said this was going to happen from the beginning, but it's nice to see it verified by an expert at that level. People are always talking about theoretical differences, but a lot of times "in theory" and "in practice" are 2 different things.
So -- I'm going to let the games decide
Hopefully that'll put anyone that was worried about theoretical RAM specs at ease.
Okay so you have said "it's nice to see it
verified by an expert" - Nothing has been verified by anyone. He clearly states (see the link in op) that "I haven't done really rigorous benchmarking". So no tests have been done from which he can base his comments.
Lets assume that he is making this assumption that both are "essentially the same" based upon his experiences as a co-founder of id Software, which is acceptable.
There is a significant, as you say, theoretical difference, between the RAM used in the two devices. GDDR5 (in PS4) is a much faster operating random access memory for graphics processing, however, if the system architecture is developed efficiently, it can be less powerful than GDDR3 (in Xbone). So for this reason, no worries about "theoretical RAM specs" can be put at ease until the consoles are released and developers have had significant time developing for the platforms.
The MAJOR difference between the two consoles is the GPU. PS4 has a 50% higher max performance than the Xbone. Now because neither console matches high end PC specs, a comparison of performance between two GPUs (one having a 50% higher max performance) can be made on a PC. Although it doesn't give a direct difference between PS4 and Xbone, what it can do, is show exactly how much of a difference a 50% increase in GPU max performance can do.
Digital Foundry conducted this exact experiment and the results can be found in the following video: NB - The numbers on either side that are ever changing are the frames per second. Anything below approximately 26 frames per second, will translate to you noticing that the video is not fluid and you will notice a stutter/lag/jump in the video (the number 26 will vary from person to person and depends on many factors but is approx. 26).
As you can see, a 50% GPU max performance boost, does NOT give a direct 50% performance boost, but rather an approximate 25% performance increase. So in any areas with explosions or high amounts of action on the screen and lots for the GPU to compute, the PS4 will demonstrate an ~ 25% improvement in the frame rate which could well be the difference between you noticing a stutter or not.
For 50% better GPU = ~25% performance increase
So for anyone out there who is to be blinded by this guys comments, and for those who think that these technical specs are something silly, please think again.
Source of information:
1.
http://www.extremetech.com/gaming/162612-ps4-vs-xbox-one-performance-compared-using-representative-pc-hardware
2. Own geeky knowledge lol