Go with the 195. I had a 180 in for a while, and didn't have any problems but when I had to change it again I decided to throw a factory-spec T-stat in.

And yeah, when I first bought my XJ, I was quick to learn that the previous owner had used stop-leak as well and have had to restore and replace most of my cooling system. Next job will be the heater core since that's the last--and most difficult item to replace. Flush it, check your radiator fins for any leaks and replace it before wasting $$ on antifreeze just to watch it leak out more.