Thanks for the replies.
I will try do a fuel pressure test. I remember I had to replace the little regulator on the fuel rail for my e46 years ago.

Regarding the coil packs, I have tested them and they are all the same. I get very low ohms, 0.3ohm from memory. Thats across 2 of the 3 pins. The other pins give no reading (OL). All 6 coils have identical readings.

The spark plug in cylinder 5 was a little bit brown, so I have swapped the coil pack with another cylinder. I will drive the car tomorrow and see if the browning spark plug follows the coil.