I'm unaware of your 760s problems as I don't normally visit the RWD forum anymore but I do own an older 745T so I'm very familiar with 700s. It's not unusual to need to put a few bucks worth of costly repairs with an older Volvo (any of them) or any older car for that matter. Volvo parts are also costly compared to domestic car parts.
If you've made progress with your 760 (like it's now in good condition, fixed) then you'll probably be better off to keep it. A '97 850 will cost alot more money initially and I see people spending alot of money on those cars as well. If the 850 is low mileage and in good condtion, it shouldn't give you problems for a while BUT sooner or later it too will need a few costly repairs as well.