Hitting the body part multiple times per week with in your natural recovery range is going to produce the most protein synthesis and gains. That being said knowing or learning how much you can recover from is not an easy task.
If you are doing everything else right, eating well, getting your rest in, and training hard you are going to make better progress that way than worrying about a split. If you aren't already doing all of that other stuff well then I would worry more about improving those areas and just working hard when you are in the gym regardless of split. It is the things nobody likes doing outside of the gym that get the most progress.
Something you might look into though for a Natty, is PHAT training by Layne Norton - It's a program that hits things twice a week, once focusing on strength ranges, and the second focusing on hypertrophy. I would say it is an excellent program for anyone trying to get bigger and stronger whether on gear or not.