I just took the test last month and what it amounts to is a test of your inspection skills point blank.(not welding skills) (I am and have been a welder for a long time)
If you have the tenacity to exame every thing you see and evaluate what you see you can get by. (if you are prepared)
Knowing all the answers is not enough, the tests are not that simple. Some of the questions may be very simple to some one whos been around the industry for a while but you may not recognize the correct answer or answers.
There for what ever code you choose is not so important as your ability to find and interpret it needed information.