Sure, it does depend on the road and having been (presumably, down) it before helps. Having been down it a lot helps even more.
For me, the dividing line is when I wonder if I could get up and walk away were I to go down hard.
That's "dividing" as in "I start to think about it" not "OK, I'm going to slow down now"
Some of us just have that "Need for Speed"... pretty stupid, really.