Great research Clowntime. That was very interesting. I imagine that is another one that will never get repeated.
I would guess that it's Chuck Klein, who had 20% more OFA's than Barfield in only about 15% more games, but we don't know what his innings total was.
If we just go with games per assist.....
Klein 1600/194=8.24 games per assist
Barfield 1387/162=8.56 games per assist
So I think you hit the jackpot with Klein. Klein had 44 assists in 1930 and it got him a -3 arm.
As an aside, you may want to consider the problem of which two outfielders had seasons of 150+ games in the OF with one single solitary OFA.
This one should be an interesting challenge.