I have a Sapphire 870--and I love it! I was doing some FMQing with it yesterday and it turned out beautiful. I also have a Viking Designer SE, which I also love. The extra space in the harp with my 870 is so nice to have. My husband was adjusting my 870 and needed it for a day, so I went back to the SE to do some of my FMQing. I felt so cramped in there--couldn't wait to get my 870 back. I used to use the SE as my primary machine, but am thinking it will be the 870 now. I will use the SE for my projects that need embroidery.
You might be able to get a pretty good deal on an 850, as they are coming out with a new updated model, the 855. The only difference between the 850 and the 855 is the 855 has a decorative tapering stitch. I chose the 870 (instead of the 875...) because I doubt I would use the tapering stitch anyway and I saved a lot of money.