I like my kitchen counters for cutting. They are 36" and I'm 5'2". I always stand when cutting, gives me better leverage. Since you are having it custom made, how about asking the carpenter to make a roll out drawer or shelf unit that fits the leg room area. That way if you did want to sit for a particular task, you could roll out the small unit, then put it back when you were done.
ETA: i agree with eastermarie. You need to make sure there's a toe kick, or deep overhang.