For the most part, the 49ers depth chart is relatively settled.  We know who will be starting at corner and who will be coming in as the 3rd DB.  We know our quarterback, our running backs and so on.  Wide receiver certainly is up in the air as we've discussed ad nauseum.

Along the defensive line, there isn't uncertainty, but there are some interesting pieces-parts to mix and match depending on the situation.  The depth chart has been updated since final cuts and we're left with two versions according to ESPN and the 49ers home page:

49ers home page
LDE: Ray McDonald - Kentwan Balmer

NT: Isaac Sopoaga/Aubrayo Franklin (injured) - Ronald Fields

RDE: Justin Smith - Kentwan Balmer

ESPN
LDE: Isaac Sopoaga - Kentwan Balmer

NT: Aubrayo Franklin - Ronald Fields

RDE: Justin Smith - Ray McDonald

I pulled up my TiVoed 49ers-Bears game from Week 3.  Since the starters were slated to play into the third quarter, it seems like we would get the best idea of who is where on the defensive line; particularly since everybody on the line was healthy going into the game.

When Fox ran the defensive players across the screen they went with ESPN's depth chart. However, that doesn't tell the tale if you look at the first Chicago series. 

First play of the game: They used the  4-3, lining up McDonald and Smith on the ends, with Franklin and Sopoaga playing the defensive tackle positions.

Second play of the game: They switched to the 3-4 with Justin Smith lined up at outside linebacker.  Franklin played nose tackle, while McDonald and Sopoaga played on the ends.

Third play of the game: They went with a nickel defense on 3rd and 8, with two linebackers and four down linemen.  The four linemen were lined up with a big gap in the middle and two on each side of the gap.  They went with Justin Smith and Ray McDonald in the defensive tackle positions and Roderick Green as one of the defensive ends.  I think Parys Haralson might have been the other but I'm not sure (might have been Balmer).  Even though both our linebackers they were clearly down linemen rushing the passer and both have filled this role in the past.

This is clearly a small sample size, but even before this it was pretty clear the 3-4 and 4-3 would be mixed in together liberally.  On the one hand, as the three plays above show, that certainly could create some confusion as to the roles of each defensive lineman (and even some of the linebackers).  On the other hand, the team will have plenty of opportunities to mix in fresh personnel.

So this hasn't really answered our initial question regarding the depth chart.  Ray McDonald clearly will be receiving a lot of playing time and the team has indicated they'll mix him in quite often with Justin Smith.  His biggest impact will be in pass-rush situations, but he's got the talent to be an every down lineman.

The 4-3 depth chart is easier to predict since they can move Sopoaga over to defensive tackle and slot in McDonald.  Smith is on the line and Parys Haralson/Roderick Green fill the OLB slot.  In the 3-4, I wouldn't be surprised to see Justin Smith getting more than half the OLB snaps in order to keep McDonald in the game.

The 3-4 is not designed to create a lot of defensive linemen sacks.  The down linemen open the door for the linebackers to make plays.  However, due to the mixture of defensive fronts the 49ers will be showing, I believe Ray McDonald is the key to the 49ers pass rush in 2008.  He's got a chance to be the impact pass-rushing defensive lineman the 49ers need.