I love Aurifil 50/2 for piecing. haven't had any breakage problems, none while sewing and none (so far, fingers crossed lol!) in finished quilts.
I've quilted with Aurifil 50/2 as well (medium size FMQ meanders) and it looked a bit skimpy for my taste. But it's not breaking, which is the main thing. There is an Aurifil 40 weight specifically made for quilting, which I haven't tried yet.
I use my 90 topstitch needles with everything, including Aurifil thread - even with Presencia, a 60/3 thread that is even thinner than the Aurifil!