If we do trade the 6th pick in the draft here is the chart of what to expect to in return. As an example I have seen some say we trade down number 6 to 10, With that we would get the 10th pick plus we should expect no lower than pick #60 in the draft (2nd round pick) because the difference between the 2 picks is worth 300 points and this is the value of pick #60.
NFL Draft Point Value Chart
So anything lower than the 60th pick would not be in the Redskins favor for the trade scenario above (so getting a 3rd round pick for trading from #6 to #10 would not be a good deal for the Skins) - we would need to have a 2nd round pick to do a deal like this.