I used the WAR ratings and the MLE equivialents from the Hall of Miller and Eric's website to make this spreadsheet. Then in excel I used the conditional formating color scale on each individual player seperatly to determine the best to worst seasons. I then used my replay machine Dave Koch's PC baseball to create the players as follows. I copied the MLE player and renamed them to their MLE Negro League player and adjusted his ratings based on the spreadsheets determined percentages. (see legend below). I would like to state first their is probably no way to know how a player would have actually perform when placed outside of their actual "real life" environment. So yes this is all hypothecial. Now a disclaimer, I tried to not go by stories or hearsay. For instance Josh Gibson was knicknamed by some as the "Black Babe Ruth". That is neither fair to Babe or Josh. Why because Babe didn't play catcher and Josh wasn't a pitcher. I liked the Hall of Miller and Eric's comparsion better. They though Josh was more like Jimmie Foxx. Jimmie and Josh both started as catchers and moved to first base for one, secondly they awesome batters, but not Babe Ruth. So with that in mind and using the colors mentioned below. When Josh was at his best he would be more like Jimmie Foxx at his best and when is wasn't he would percentage of Jimmie. I also used one more source for comparisions I found on the Bleacher Report website. So enough disclaimers. Let's get on with it. Click on the spreadsheet below then arrow to the right to see more seasons. 

Legend for below chart: dark green=110% or best season, mid green=100%, light green=90%, yellow=80%, dark salmon=60%, light salmon=40%, red=20%.