It's interesting that machines are all different, so much so that sometimes you'd think they had individual personalities!
I say this because I use Gutermann thread most of the time on my Designer SELE and I used it on my Sapphire 850 when I had it. My machine seems to be pretty good with thread and only gave me grief when I tried using metalic thread. Too bad.
I had a Sapphire 850 as my first machine after not sewing for years and loved it. Never had any problems. Unfortunately, I got spoiled for the newer machines and traded her in for the Designer SELE which I love too.