Im not surprised you cant comprehend my posts when you cant spell "inefficient" How can you explain the intricacies of efficiency when you cant spell it.
Do you think anyone cares about power use when buying desktop GPU's? My next PSU will be 1000w My 7970 runs at 70c on 1125/1700 24/7. Who cares about 30w of power use?
I don`t think you are capable of understanding it.
Let me explain it easy for someone like you:
7870: Efficient. Use little power but produce a lot of FPS with as little power as possible. Heat follow power. GPU not very hot
7970: Not efficient. Use a lot more power than 7870, produce a lot of FPS too, but also use a lot of power. Like any GPU, heat follow power, GPU produce more heat than 7870.
7980: Let us assume AMD made bigger GPU based on Tahiti (7970). More cores. What do you think will happen to the die or the silicon? Think efficiency and heat.
You can`t just make a bigger die and slap on more cores if you have a horrible inefficient chip to begin with. You have to cool off that single chip too, and you can only use one fan. What you can do is overcome this problem by building a dual GPU card, spread the cores apart and have more fans to cool them off. That is what AMD did. And that is their only choice for their inefficient Tahiti. They made 7990, and if you remember their strategy plan for 2013 is have 7970 as their highest end single GPU and target Titan with dual GPU.
You see how it all fits together?