The farther the better I say. I have a 29 inch arrows. One of my bows is a 28" draw (7" brace) and the other is a 28.5" draw (8" brace). It's not a problem with the 7" brace bow, but I have to concsiously keep my fingers tucked in with the 8" brace bow. I've tried longer arrows, but they fly like crap.
I know it may look goofy, but I've never understood why bow manufacturers don't make some sort of extended arrow shelf that your hand completely sits under. Some guys don't think twice about having the broadhead sit just barely past the rest. To me that's like keeping you fingers in front of but just below the barrel of the gun. The bullet "should" miss it, but...
Emrah