The 87 to 92 thermostat is of little difference down there in south texas. Since your engine is going to pretty much always be hot during the day you drive it doesn't matter if it opens at 180 or 190. It will usually be over that. However, up north where it gets quite chilly, having a 190 will make a big difference in the winter time as to how fast you get heat.

Now an OEM and a 3rd party thermostat, the difference there is important. A failed thermostat that is shut will cause the coolant to boil in minutes resulting in a pressure spike that will usually blow the head gasket. That is not a fun fix.

As a side note, with the way volvo designed some of the things to fail first on the car to save money (like the linkage on the AWD's to the rear axle that is supposed to break and leave the bevel gear intact) you think they would have done something similar to prevent head gasket blow out. I'm not sure of the best way to do this, but perhaps a pipe with a blowout pressure of 25-30psi or even blowoff valve a couple of psi above normal operating pressure (which i believe is 15psi)...