Wednesday Water Cooler: When Is It Ok to Own a Team's WR or RB Duo?

Would you be happy having the 11th and 13th best fantasy backs on your team? Or how about the second and 12th best fantasy wide receivers? What if they were on the same NFL team? 

Were Randy Moss and Wes Welker the only dynamic duo to consider? Would you own DeAngelo Williams and Jonathan Stewart, or Ricky Williams and Ronnie Brown?

Statistically there are only a few worth having, based on last year's fantasy numbers from ESPN. Many of those are not viable this year. Willis McGahee and Ray Rice come to mind.

What are your thoughts on who is worth it or who is not? Who may be soon?