I sometimes use 12wt for machine quilting and other times 30wt, depends on the quilt and the quilting pattern. My machines (Bernina and Viking) have no trouble with either and I match the top thread weight in the bobbin (yes, even with the 12wt). I like heavier threads (I use 40wt for piecing), but use whatever
you like. If it goes through the eye of a needle without shredding, you can quilt with it.
Regarding needle size for heavy threads, remember that the channel size is just as important as the eye size. And you might want to increase the stitch length for quilting with heavy threads. It looks more balanced with longer stitches, more proportionate, and straight stitches are much more important when the scale of thread and stitches is increased. Take the time to get everything just right, and you'll love the result. I've used Sulky cotton in both 12wt and 30wt along with DMC perle cotton in 12wt and really want to try perle cotton in 8wt to see just how far I can push the edge of my envelope.
