Now that I have the database code working (I still need to verify my latest computation) it appears that the longest win is a mate in 40 moves. In 8x8 chess, the longest win is 33 moves.

OK, the contest for guessing the longest win can officially start. Post your guess here. The person who submits the position resulting in the longest number of moves for white to win will receive a stainless steel Gothic Chess mug for the price of shipping.

And here are some stats of the latest run, assuming everything verifies properly when I do the test tomorrow:

Mate in 1 move: 2400 positions
Mate in 2 moves: 1324 positions
Mate in 3 moves: 3247 positions
Mate in 4 moves: 16136 positions
Mate in 5 moves: 49640 positions
Mate in 6 moves: 60757 positions
Mate in 7 moves: 78414 positions
Mate in 8 moves: 58897 positions
Mate in 9 moves: 57946 positions
Mate in 10 moves: 60434 positions
Mate in 11 moves: 110168 positions
Mate in 12 moves: 168635 positions
Mate in 13 moves: 254549 positions
Mate in 14 moves: 294188 positions
Mate in 15 moves: 261796 positions
Mate in 16 moves: 213463 positions
Mate in 17 moves: 171700 positions
Mate in 18 moves: 179002 positions
Mate in 19 moves: 193550 positions
Mate in 20 moves: 275013 positions
Mate in 21 moves: 421860 positions
Mate in 22 moves: 618981 positions
Mate in 23 moves: 743712 positions
Mate in 24 moves: 793462 positions
Mate in 25 moves: 768425 positions
Mate in 26 moves: 880231 positions
Mate in 27 moves: 1022307 positions
Mate in 28 moves: 1397010 positions
Mate in 29 moves: 1849137 positions
Mate in 30 moves: 2444455 positions
Mate in 31 moves: 3131093 positions
Mate in 32 moves: 3661812 positions
Mate in 33 moves: 3506075 positions
Mate in 34 moves: 2590711 positions
Mate in 35 moves: 1388359 positions
Mate in 36 moves: 482325 positions
Mate in 37 moves: 101621 positions
Mate in 38 moves: 13804 positions
Mate in 39 moves: 1788 positions
Mate in 40 moves: 245 positions