I've been reading up on OTs and I came across this article which uses some real, but very limited, stats to analyze draft position and future performance for QBs, RBs, and WRs. Some previous Rams WRs are named!
I think the article was poorly written and it needs a good editor, but some of his findings are interesting. Skip to his conclusions. The summary is that 60% QBs drafted in the 1st and 2nd rounds, have been more successful than the QBs drafted in rounds 3 - 7, BUT, for RBs and WRs, the opposite is true.
Note that his sample size is very small, and he only covers years 2008 - 2012.
Implicitly, I think he is suggesting that if you don't need a QB, are set on defense, but really need a stud RB or WR, then trade your 1st and/or 2nd round pick for a handful of 3rd thru 7th rounders (plus whatever else you can get).
"Success or Bust" by Connor King
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fisherpub.sjfc.edu]