You seriously make no sense at times and I struggle to understand what you are driving at....
Trying to decipher your comment, if I pointed at "one shoe fits all", surely I would have only said Titans? But I didn't now did I, as I also mention 780 6GBs and that is a pair right there. Maybe read before posting nonsense?
Now then, back to what I was saying via 7950s, you can not turn the details up enough to allow 4 7950s to stretch their legs at 4K, as they will clearly run out of VRAM in a number of games and that even includes some older games (Far Cry 3 for instance). You said a pair of 7950s, now if you had watched the video, Tom talks about Pixels per degree of vision and in a typical scenario, you are sat at roughly 20" from your screen and 4K gives you 35.6 of a possible 50 PPD that the human eyes can see, so when people say "But you don't need all that AA because your eyes can't see it", well research has proven that we can and in fact, can see more as well.
So if you bought 2x7950s or even 4x 7950s and play at 4K, you would need to turn the settings down and in turn, this is lowering your gaming visual experience. With Titans/Titan Blacks/780 6GBs/290X 8GBs, you will have enough VRAM to experience 4K at its ultimate setting and using my self as a case point, I want to see the pretties and I don't like to compromise.
These are basics that I thought you would know, as you have been beating the VRAM drum long enough now.