Devin Hester would be the downside example is use.
ETA: or Dante Hall.
I thought of Hester... Then I looked up his numbers. Hester is a poor example as well because he didn't even play a down of WR his rookie season. Then in his 2nd season he only had 20 reception, 299 yds and 2 TDs. So, Patterson has already beaten the numbers he took 2 years to produce by light years in just his rookie season.Hall is the same story, only worse. He didn't play a down of WR his rookie season, either. He also played hardly any his 2nd year amassing 0 receptions. His 3rd season wasn't much better amassing 20 receptions, 322 yds and 3 TDs. Again, Patterson is light years ahead based only on his rookie season.
Terrell Ownes seems like a much better comp based on his limited experience in college and rookie season. He didn't tear up ST like Patterson, or have the rushing numbers but from a learning curve and physical ability standpoint I think they were most similar of anyone mentioned yet. Hopefully Patterson doesn't have the metal issues to go along with him...
TO had 35, 520 and 4 his rookie year.
Muhsin Muhammad or Laveranues Coles might also apply.