P7 is generally thought to be a good fit with P2 (I assume that you have passed P1 and P3 already)
The higher level audit paper involves a sound knowledge of IAS / IFRS
You say that it is your intention to apply for a UK practicing certificate so just make sure that you enter for the UK variant in both P2 and, if you choose it, P7
If you have visions of specializing in taxation after you qualify, then P6 would make a lot of sense
I know very little about P5 so am reluctant to point you either towards or away from it