I'm not a big fan of some of these rankings. Take Reeder for example... he may not have a lot of missed tackles because he was either already taken out of the play, or he made the tackle and was dragged another 5 yards after contact. Who knows? All I know is that the Rams linebackers are a big problem.
Rams have been stupid with ILBs for a long time now. They have gone through "chase" backers who are basically souped up safeties, guys like Ogletree and Littleton, who creatively find ways to chase the play by letting runners take an angle that results in yards given up. Or guys who have limited range or instincts in Reeder (instincts) and Jones (range). None of these guys would ever start for a defense that knows what it's doing in finding ILBs like SF or Baltimore. Those teams find dudes who have instincts for the job but also range, and coach them up.
Speights is the first ILB I have seen in this defense in many years who has actual instincts and willingness to fill hard on the interior but also the range to get outside and make plays. Hummel by the way also looked good in preseason, but is more the chase type, which is fine for the pairing when you have a guy who can lock it down next to him. Saying he's a chase type is to mean that he can fill occasionally and get a stop for you, but you don't want him doing that as a primary role because it won't go well. Hummel is very much a souped up safety.
Now I fully realize that Speights might not be able to sustain what he was doing in preseason into the regular season. But the key here is that I know what Reeder is. Which means Speights at least has a chance to be that factor we have lacked back there for so many years. So play him ffs.