I have both a RWD '89 740 Wagon and a FWD '95 850 Sedan. I feel equally confident in the snow with both cars, as long as I have a good set of four snow tires on the 740. (I only use regular all season tires on the 850.) I will also put a couple of 50 lb bags of sand or salt to add some weight over the rear axle in the 740 as I normally drive this car with no other load in it. I currently have a set of Dunlop Graspic snow and ice tires that are performing well. You can research tire brands at Tirerack.com (I live in Northeast Ohio)

You might ask if it has a limited slip differential. This would be a plus for RWD traction but not a necessity. My 740 does not have limited slip diff.

I don't know that Volvo has a significantly better RWD design than other RWD cars, but the RWD Volvos have a very durable drivetrain. Also, typical repair costs should be lower on the RWD than on the FWD. One of my favorite features on the RWD 740 is the very small turning radius - you can make u-turns that you would never try in another car. You will not find that on any front wheel drive vehicle including Volvos.

I would be more concerned about how this car has been maintained if you plan on buying it.