I cut mine about 3-4 feet. Beeswax does the trick for me for preventing numberous thread tangles. I still get a few but not as many as before when I use the beeswax.

I cut all thread the length of my fingers tips to my inner elbow and then thread 6-10 needles. I find I work faster with the shorter threads and there is no tangling. It is even faster if a DD or DH keeps on threading needles as you empty them - but that does not always happen.

I use about a 3 foot length and run it thru Thread Heaven.