I could see having a level 6 coach on a draftee of that quality for the first 2-3 seasons when they train the most, maybe to get a little extra if your building up secondaries. Otherwise, as Azariah said, a 4 or 5 is just fine. In fact, I've never noticed a difference from 4 to 6.
"Well, no ones gonna top that." - http://tinyurl.com/noigttt