For me the number is pretty low...a 23 mile day hike but I'm only a section hiker and never have the opportunity to really get my trail legs under me.
The reason I ask is I am reading Texaco's journal this year http://www.2180miles.com/trail-blog and in honor of his grandparents 60th wedding anniversary and because he was on the trail and couldn't get them a present, he hiked 60 miles in 20 hours and 32 minutes
That's just under 3 mph for 20 straight hours! Now granted he did it from Harpers Ferry north bound which is a flat section but still. That's getting it done!
Also, if anyone would like a good journal to read his is a good one. Posts almost every day and is a good writer.