The only thread I've ever had an issue with on my 7700 is Superior SoFine. Lots of breakage and tension issues. It loves Aurifil 50/3 and Isacord poly. It will sew fine with Masterpiece but the stitching looks a lot better with the Aurifil.
Needles - I'm using some Schmetz ones I bought more than 25 years ago (yikes!) - I happened to stock up back then. Again, had trouble with Superior titanium.
Michelle