I wouldn't go any lower than the middle hole in the rear, or 3/4" down in the front unless ya want to scrape.
Mines down a hair over 1" in the front, and I have to be careful on speed bump....I actually get up off the bike and put my feet on the speedbump when I go over.
Handling is not terrible when ya go 1", but deffinately noticable.....at 3/4 it's not to bad at all....actually barely noticable.....unless yer last name is Bostrom.