My Janome 6600 came with the "blue dot bobbin case" and I had the great same results with FMQ!

I like Sulky blendables,King Tut,Valdani. I use a 16/100 top stitch needle when I am machine quilting on my regular sewing machines. I own a Viking Sapphire 875,Bernina 1031,Pfaff 1222E,antique Singers. I don't have any trouble with the threads on any of my machines as long as I use a top stitch needle.

I have a Pfaff 7550 and I have tried many different threads. It seems that my machine works better with some threads.
I tried Aurifil but it kept jumping out of the bobbin and I kept having jam ups. I tried Connecting Threads because of the price but I seem to get alot of breakage and a ton of lint. The Gutterman is not bad but I have to say that my favorite that I keep coming back to is Mettler Silk Finish Cotton 50 wt. I don't get much lint, no thread breakage and I really like the look of it.
I think it is the fact that home machines were not intended to be used the way we use it for FMQ--constant high speed for long periods. I clean my bobbin case with every new bobbin and I change the needle about every 5th or 6th bobbin.
I do this no matter what thread I am using. I also oil the bobbin case about every 3rd bobbin when FMQ.

It's probably your needle...check Superior Threads needle charts.

I tend to buy other brands than Guterman. My Pfaff doesn't like it at all for any sewing.

Yes it was Mary Buvia. What I didn't mention, was that the Top Stitch needles have a larger hole than most other needles, and the thread slides in and out of the needle resulting in less stress on the thread,

What weight of Sulky cotton are you using? I use it quite often to quilt on my 6600 without a problem. It's not my favorite thread (a bit to messy/linty), but I have several spools so I use it.

My Pfaff also does not like Aurifil. I thought it was just me! Mettler Silk Finish cotton works well in my machine. I also use one of those teflon washers in the bobbin when FMQ. I still have thread breakage once in a while. I'll have to try the top stitch needles as suggested.

i love the king tut for machine quilting

I don't like Sulky either. seems to break a lot. I have been using a lot of threads from Superior -- love their "rainbows" variegated ones. And the metallics work well for me (I have a Janome 7700)