The 850 is always going to loose in a head to head comparison with a similarly maintained red engine car. The interiors on the 850 always seem to explode out past 150k or so, they are way too plasticky and the driver's leather seat panels always wear out. Even if they both had the same laundry list of items that typically go bad it is going to cost you more to maintain the 850. Just off the top of my head the things that I routinely recommend on 850's:

Heater cores
a/c evaporators
engine mounts
torque stay bushings
control arms and/or bushings
breather boxes
radiators
timing belt tensioners and idler pullies
water pumps
fuel pumps
ignition contact plates
odo gears
dash light bulbs
struts and spring seats
engine oil pick up seals
assorted rotted vacuum lines
abs control units
axles and boots
ball joints
front hub/bearing assemblies

All that being said, seeing as how I own and run a Volvo repair shop, I wish the whole darn world drove them. There is no money working on good cars.

Mark