Only two DT's have been between the beginning of the 4th round and over half way through the 6th round and one was a grade 30.
The Broncos took a safety with their first pick in the 4th round. Grade 75. A few picks before that, the Bills picked up a safety. Grade 54. Thirteen picks later, the Jags pick a safetly, grade 30. In the 5th round, Safety's started dropping like flies. 6 were taken.
A guy with a grade of 30 will be picked and two picks later, a guy with a grade of 80 will be picked.
The draft is highly subjective, and one man's trash, is another man's treasure.