I found performance the hardest exam. But that was many moons ago when PPSC correspondence courses written by Mike Longhurst, were the normal method for self improvers working, with studying on days off etc. The notes were not the most user friendly? These days internet access : junior birdmen don't know how lucky they are. Far better learning medium.
No short cuts. Put in the effort and you will pass.
It would have been so much easier to have a good teacher using talk & chalk explaining the LOGIC (and the rules) of it all.
Then, pass Performance A, and there was no need to pass any other performance group exam -aeroplanes.
That changed in1988 when this "exempt all others" rule was ended by the UK CAA.
Grandfather rights applied to ac changes within perf A, but new smaller ac types required the specific group performance exam. Eventually I ended up passing performance exams in C,D, E.
Prepare really well and success will follow.