Been a long time since I did FMQ this way, since I got my longarm, but I remember having a long learning curve trying to get the tension right. I tried lots of different threads, and had luck with most ... eventually
Sounds like you found something that works for you, so I'd go with it. I do recall having to play with the tension on my bobbin, not just the top tension. And, you're putting your feed dogs down, I assume?