I've never done the magical 1000, but low 900-ish a few times. Not by choice generally, but because i need to be somewhere or turn 2 days into 1 to get home sooner at the end of a long trip.
I find anything under 600 to be comfortable and sustainable for me. i.e. after 600, I don't look at the bike with dread the next morning and can do it multiple days in a row.
2002 KLR650 - 2007 HD Electra Glide
'It doesn't matter how big a ranch ya' own, or how many cows ya' brand,the size of your funeral is still gonna depend on the weather.' Harry Truman
"Death smiles upon us all, a U.S. Marine smiles back"