I'd agree with one addition though.....
What's "ample" for one, may not be for another.
I've been getting 5 hours of sleep as long as I can remember.
Just the way Im wired. I adapted to this many moons ago and feel fine and also feel my gains are not hampered.
I also dont have a physically demanding job so I would imagine I dont need as much rest as a construction worker who works out.
By the way: Can anyone really know IF their gains are in fact hampered or better yet, if they gained MORE b/c they slept more? hmmmmm Think about it
Moral of the story is listen to your body. You DO need rest but how much is for YOU to figure out and unique to YOU