Terrain definitely makes a difference. Here where I do most of my hunting in MS woods, I can hear the drumming once they get to about ~60. Furthest I remember in MS is ~80 yards in some open bottomland hardwoods before green up. However where I hunt in the Missouri Ozarks, I can usually hear them a tad further. The understory isn't near as thick there and I just believe those larger framed birds drum a bit louder. Farthest I know for sure has been ~120 yards in Missouri woods. I was closing the distance on a gobbling bird, heard drumming and immediately plopped down. Wasn't long before I saw him coming straight my way. Last year one evening in Nebraska I watched a Merriam's from about 70-80 yards away strut in a wide open meadow. I could hear the drumming super clearly.