Cathay Pacific Asia Miles - GF Award question

As it seems to be impossible to get any seats on CX between JNB-HKG (first and business always full and soon they change plane and then only buz), how many miles I would need for first or business class with Gulf Air between JNB and HKG via BAH?

You would need to add the required mileage together...

JNB-BAH-HKG and from that total, you will be able to see the award zone you need.

http://www.asiamiles.com/en/redeem/flights/charts/#2

It looks like a ZONE E.

Note that you may combine GF and CX flights together... ie go on GF, return on CX.