I got the 85% from Radical Brewing
by Randy Mosher. He says 85% for LME and 65% for DME.
I saw another site (that I can't find right now) that said 80% and 60%.
Someone here posted a link to this site
, where the suggested numbers are 75% and 67%. Who knows which is right, tho 3/4 and 2/3 are definately easier to work with.