I purchased the Viking Sapphire 835 just over a year ago. I took a class at the shop I purchased it from. Learned quite a bit, this machine has quite a few more bells and whistles than I'm used to! I love the alphabet and the ability to make "quilt labels" that I can then decorate with single motif embroidery designs. I have done some garment repair, various types of quilt piecework and the majority use, main reason I bought it, learning how to free motion quilt. The additional space in the harp or throat area is fabulous!
As for repairs, my newbie is due it's first year checkup, but I haven't had any real problems with the machine, just had to learn that it's a bit cranky if you don't thread it just so! And with the FMQ, I have a pretty good idea what an empty bobbin sounds like! If you can afford the price difference, I'd say the 875Q is a good choice. Especially if you are getting it from a good shop!