I would suggest considering P4, P5 & P7. The tax one won't be a good choice. Also ACCA doesn't provide you with a Pakistan variant for tax paper so what's the point of studying UK tax when you will be working in Pakistan in future? So this is what you must consider.
If you have difficulty choosing from these 3 then here is some guidance for you:
First of all consider what interests you the most. Secondly, if you don't have practical experience in any of these areas (option papers) look at the previous exams you sat ( F5, F8 & F9) and see your performance. So you'll see 3 things in selecting the ones for you and these are:
1) Your interest
2) Your experience
3) Your performance in the basic skills level paper relating to these option papers
After considering the above criteria what I consider to be good combinations are:
P7 & P4/ P5
P4 & P5
If you do want to go for P6 then I won't recommend taking P6 & P7 as these are entirely 2 different things and you may end up getting into one. So choose 2 papers which can work well as a combination.