We have needle 15 on all of our machines setup all the time for metallics and we don't run anything else on needle 15. Good thread, large eye needles and let er rip... You will have to play with tensions but only once. Depending on your machine, you may have to do something to "condition" the thread before it enters the thread path. And we never slow down the machines for metallics.
On our tajima machines, by the time the metallics make their way through the thread tree and into the first pretensioner, they are pulling nice and straight.
On an old toyota machine we would actually set the cone on the floor behind the machine.
On a couple of older melco machines we had good luck with threading through a styrofoam peanut just before the thread tree. That seemed to take out any twists.
Oh, and the reason we don't go back and forth from metallics to regular threads, it does seem that the abrasive nature of the metallics is hard on the thread paths over time.
Find what works in your shop and stick to it...