From my experiences drafting individual defensive players, I have found that rounds 4 or 5 starts it off. LB's will be the first to go. (Lewis/Urlacher/Thomas/Brooks) could all be worth a 4th or a 5th round pick. You could probably go for a few of the top DE's if you wanted to in round 5 (Taylor/Rice/Peppers), however I would probably hold off unitll round 6 or 7 for these guys. The rest of the DE's/DT's are very unpredictable, I would rather start looking at LB' or DB's before I put my money on a lineman who may only get 1 tackle in the course of a game.
As far as DB's go, I say look at the top Safties. I had (Rod Woodson, Adam Archuletta, Roy Williams and .... oh yea Tony Parrish) These guys did great for me, and helped keep my team in many games where I messed up my offensive team. What I look for in a DB is a player who can and will step up into the "box" and hit the RB's. Trying to guess what DB will get the most picks this year is like, trying to figure out what women really want. I was drafting these guys in rounds 9 and 10 while ohters were taking big name DL's like Sapp and Kearse. BAHHH I think all of my DB's out scored these guys in my league, and my scoring was similar to yours. Only major difference was we had 2dl 2lb and 2 db.
My advice to you in this is take the guys that are consistant, and if you are sitting with the choice of Brooksand a so-so receiver, in the 5th round, go for Brooks you will be happy in the end. Good luck in FF this year. If any of you disagree I would be happy to hear what you have to say.