I think realistic would be -50 I tried the default settings and though the game played great out the box I started to hit to many homeruns so I dropped everything to -50, tamed everything for me . But what may work for me may not work for others.
I think some of the sliders may even contol different things for example when I had foul ball frequency at 0 I had lots of hits and foul balls but not a lot of k's but when I raised the foul ball freq I got more strikeouts.
I'm not using pared's sliders just so people don't get confused.