nothing short of phsyically trying it out urself will give the right answer...each car is different. but the 850 wheel well is surprisingly tight (70 series were enlarged)...and slight changes may mean rubbing. it might fit...but i doubt u'd be able to use chains. c if u can use cables instead. they have a slimmer profile than chains. if u'r gonna use the wheels from the 245..make sure they have proper offset, if not, just get some cheapo steel ones that'll fit the 850

I have used 205/60R15 all season tires on my '95 850 sedan without any problems. As you mentioned the OD of these tires is not much larger than the 185/65R15. They do fill up the wheel well and I do not drive the car very hard. I live in Northeast Ohio and have never used snow tires on my 850. The front wheel drive seems to get me through our typical winters here. I do use snow tires on my 740 Wagon. Since you already have the 205/60R15 snow tires, I would go ahead and put them on the 850 and see how they perform. If you live in a very demanding winter climate, you might notice that the 185's would perform better in snow than the 205's.