All depends when you are going to do your test. If you're in no rush, you'd be better off doing lessons with an instructor to take into account the off-road section of the test. As I said, DAS won't matter to you because of your age, so it's up to you when you want to do your test. I'd personally try and get it done before the end of the month though, so you can sit the "easier" test, just ring an instructor and ask him can you do a quick assessment. If you're confident about your bike skills, you should fly through it
EDIT> Just seen your last post. Ever considered an XR400 w/ superm