This one is 5 pieces only.
I'm curious if GMs could win in 40% of all positions.
http://en.wikipedia.org/wiki/Rook_and_bishop_versus_rook_endgame
Most of these positions are drawn by the 50 move rule, regardless of whether the tablebase can find a win.
In practical terms, trying to play out a Rook and Bishop vs. Rook endgame seems unreasonable.
I heard Noam Chomsky once say: "The only thing a chess playing computer can do for you is ruin the game of chess."