The idea that "4 oz of juice 3-4 times a day shouldn't be exceeded" is new to me. Where can I read up on this? Perhaps you mean 4 oz per 50 pounds of body weight ;)
I know you can OD on sugars, but if you stick to mostly spinach, cucumber, celery, sprouts, cabbage (mmmm... cabbage) and such, you don't get that sugar-high and then the downer that follows.
I'm used to juicing a good 2 litres of juice in the morning and storing it for the day (probably only good to do this if you have a twin-gear juicer). I guess thats around 4 times the amount you suggested. How can you tell if you are OD'ing?