Trading down might not be the best move for the Rams, according to ESPN's Mike Sando, but taking a DT might not be the best move either. Here's the case against trading down "They already have nine draft choices, including three of the top 65 and four of the top 101. The second overall choice gives them an option unavailable to any other team: taking the highest-rated defensive player in the draft."
Sando points out this tidbit: "Teams have taken only two defensive tackles among the top five picks this decade: Gerard Warren and Dewayne Robertson."
Dorsey and Ellis are the only top-10 worthy DTs in the draft this season. DEs taken early in the draft have a much higher success rate: "Since 2000, 11 of 14 defensive ends taken in the top 13 picks have met or exceeded expectations set by Scouts, Inc. The success rate drops off for defensive ends taken later in the first round."
This goes along with Sando's later post, noting that the Rams could be a playoff team this season, if the o-line stays healthy and they draft well.