A tool like the excellent Bristol ATP online database will give you an idea of your ability to pass the exam. Note that on the Bristol database all questions are worth equally when marked. Also, take a look at the JAA specimen papers to which you can find with answers on the public Bristol forum. The first questions are normally just 1 markers while the last questions are more likely to be more than that.
I think that I know before entering the exam room if I quite likely will pass or very likely will pass an individual exam. Those I thought that I was quite likely to pass I got scores in the low 80's while those I was very likely to pass I got more than 90 percent.
It is not the end of the world if you get 74%. You only have to add another percent of knowledge till the next time you take the exam.