AMD can't afford to make a super high end big chip. They don't have a big enough foothold in the super computing/professional market to make it financially feasible. That being the payoff from such a heavy r and d move and the number of wafers at 20nm these take up, would be wasted unless they sell a lot more professional cards.

With the cash reserves so close to the breaking point, its a move AMD can't afford. AMD will not take the huge monolithic chip route unless they have more guarantees in the professional market. The only way AMD is getting a 60 percent performance increase is through 20nm. It isn't happening at 28nm.

It seems convenient for AMD that these rumors pop up just when the gtx 7xx series is coming out.