I quilt quite a bit with monofilament thread, especially when it comes to bargello. A few things I have found help. Use a poly instead of nylon... poly takes heat much better. Create a test sandwich.. to get your tension correct... its takes a bit of playing with the top tension. I use more of the smoke color than clear... less shine and is more invisible on dark colors. I have the best success using a smaller needle size.
On some bargello quilts, I will use a variegated thread, if I can find one with the colors of the quilt...it helps the bargello colors travel through the quilt.