I did nearly the same connection as the OP last month, but with the 17:30 departure to SEA.
The CX flight arrived on time, but after SQ, AZ, NZ, CI (that I know of). Immigration was complete mess, taking 1.5 hours to clear. I made it to T6 at 16:40, just in time for boarding. Thankfully, security at T6 was a painless affair.