The SQ J seat
looks great... and IMO is fine for sleeping.. but it isn't a great "seat"...
If the CX F you are booked in is the same as the "suite" I experienced (once!
) on their 747 then it is AS good a bed.. and a much, MUCH better "loungng" proposition...
Add to that the F service (which was amazing) and it really is a no brainer....
Enjoy!