In relation to above. Privet will not survive in heavy shade, so growing through the hedge is not going to happen unless one side is south facing.
Yew is excellent, if you are willing to wait 15 years+ for it to even reach the top of the hedge, never mind thicken it up. (see the millenium maze 8 years on and its about 4 ft tall and thats unobstucted growth!!!.)
Laurel as oldsplice pointed out cannot be cut tidyly with clippers, it a secateur job, used to take me 3 days to cut a 6ft laurel hedge 50ft long, and that was 3 times a year!!.
If you want to keep the neighbours out another alternative is berberis, not even a cat will try to get through that is so spiky!!!.