$1700 is a pretty bad price for the FSR disc. Assuming its all stock parts. It normally comes with XT on the back, LX everything else, and you mentioned XTR. I just bought a FSR Comp for $1500. I was actually looking at the disc too, but I don't want to replace the fork on the bike I buy, so I went for the Comp instead. I try to stay away from Manitou forks.
As for the disc performance, everyone I've asked who has used them is very pleased with them. The only warnings I would give you are these: they take a while to break in, so don't judge them by the initial performance, and don't get them if loud things annoy you. They're noisy as I'll get out when they get wet.