|So let me get this straight....|
You want to get an extra 7850 and put it in Crossfire with your existing 7850, and want to know if it would be better than the cards listed?
If so, then this is my reply: The 7850 should be good enough for most modern games in the last 5 years. What do you plan to be doing with this? Only certain programs can take advantage of a Crossfire link anyway, and in normal usage you will see 0 improvement in stuff like browsing. IMO getting a better single card is a better value than getting an extra card for Crossfire.
Another myth about Crossfire is that you add more video RAM when you link the cards. Not so. The video RAM stays the same, and if you try to crossfire different specced cards (NOT recommended!) a bigger card will try to limit itself to the smaller card. Putting two 2Gb cards doesn't give you 4Gb of video RAM, it still gives you 2Gb.
Hope this helps a bit.
Not everyone can decipher Klingon script...
chay' ta' SoH tlhe' vam Doch Daq