The thread I use the most is American and Efird D Core... a cotton wrap around a poly core. Tex 40 size. My favorite batting is Hobbs 80/20.
One hour of quilting is equal to about 2 bobbins. Yes, I'm a speed demon. I piece fast too. (My history is as a production seamstress).
My machine is the Juki TL2010Q. Love everything about it EXCEPT having to unscrew that needleplate to clean under the feed dogs. My old machine (that I still have) is the Bernina Record 830. A dream to clean, everything snaps out in seconds. The lint buildup would not affect tension in the Bernina, but it sure does in the Juki.
Thanks for all the info on thread. Gonna try switching threads and see if it helps.