In 2009, AMD needed 6 cores for Intel's 4 in highly multi-threaded scenarios. (Nehalem-K10.5)
Now in 2011, AMD needs 8 cores (Bulldozer-Sandy).
The price for the top FX 8 core (around 300$) proves me right.
And the use of the FX branding is just sad.
and eight core is priced right at a 2600K with 8 threads.