Ok you don't need 2011... If you want a I7 and dont have the money for a 3930k, then you need a 1155 socket motherboard and Sandy Bridge 2700K or Ivy bridge 3770K.. And use that extra money you have spent on 2011 towards a better graphics card. the 4890 was a great dual gpu back in the day... but its falling behind compared to the modern day single gpu's. If it were me i'd get1155 mobo and cpu and a GTX 670 or 7950/7970
Well the HD 4890 Crossfire setup has the potential to outperform a GTX 660 so i'd say thats plenty of graphics power.But in games that Crossfire isn't supported for 4xxx series cards you will get performance that's between a GTX 650 and a 650 Ti.
The other cards you mentioned will not perform nearly as well as the HD 4890 Crossfire setup.
And also there is no HD 4950 card.They don't exist.