this board is 100x100 with 2255 mines, and is rated at 255400 difficulty. I beat it this past week after only ~5 hours of playtime (quite surprising; I think the expected length for a skilled player to complete it is upwards of 50 hours)
this seed was great! it had only a couple 50/50s and with logic alone, I could clear the board from the corners to the 4 remaining islands in this image, after which a handful of fairly safe guesses was enough to finish it off.