I have the PC420PRW and I put all kinds of thread through it. I just use the regular plastic bobbins that are made for that machine, haven't tried any of the pre-wound one. Mine isn't at all picky about thread. I've put Coats and Clark Dual Duty, Gutermans, various of the Superior Threads, Madeira rayon, Isacord poly, Aurifil 50 cotton, etc. and it has handled them all very well. I've also used vintage, antique thread that I get off Ebay and it does fine with that too. Let's see, Oh, I have also used some upholstery thread (can't remember the number that tells weight) but I wouldn't recommend doing that too often as the machine isn't really built to handle upholstery. I know there are a lot of folks out there writing that the machine is picky about thread, but I just haven't found that to be the case.
Rob