Yes, the sample test on opted.org is very similar to the real thing. ppl have posted that the sample test is easier, but to me, I thought the sample test was harder than the real thing...which was a good feeling during the exam. The real exam will have a couple of surprises per subject on the test, like for bio I got a question on how old is the earth (which is 4 billion yrs), and a weird graph for physics where there was a total of 3 axises on 1 graph, and had to figure out something...cant quite remember..
But yeah, how you are scoring on the sample test should be a pretty accurate predictor on how well you'll do on the real thing 🙂 Though I gotta warn you the reading comprehension section is harder than the sample test. Harder I mean the questions, not necessarily the level of difficulty of the passage. You know how on sample test, they just ask if the 2 statements are true/false...well, on the real thing you'll see a question like choice A) both sentence and reason are false B) statement is true, reason is false and they are related C) both statement and reason is true but they are unrelated D) both the statement and reason is true, and related E) some other variation. That kinda threw me off a bit, so watch out for that. And the reading passages are all science related, for my version I got 1 passage that was pretty hard to get through, and then 2 fair ones