One important issue to consider that has not been talked about is the cap savings a team can get by trading down. Right now at #6 it would be practical to say the Redskins wil pay something similar to what the 49ers gave Vernon Davis (he was the 6th pick of the draft last year). Vernon Davis got a contract totaling $23-$25 million with $15 million in gurantees - see link below
ESPN.com - NFL - Niners make No. 6 pick Davis highest-paid tight end
So to me trading down offers an enticing benefit of not only acquiring more picks in lower rounds (which helps with depth and also gives you more chances at selecting a diamond in the rough), but it also helps minimize the future cap hit if the first rounder you do select is a bust since the lower in the first round you go the lower the required signing bonus becomes.