I'd say Bristol GS questions closely represent the real thing. If a student religiously work on the practice questions, (s)he could easily spot 'new' questions in the real exams. You've seen 99% of the questions before and the new ones just stick out like a sore thumb
Those statistics are not particularly reliable....2 bad months for Performance is probably just fluke...but if a 3rd bad month comes up, maybe the CAA is actaully doing something about it.
Otherwise, if you simply keep doing practice questions, I think you'd be alright.
Gangi þér vel!