I don't have any real facts to back it up, just what I've heard 'round the campfire. A lot of my buddies are diesel geeks, they love hot temps.
Warmer operating temps would improve a gas engine's lifespan similarly, but I'm not sure at what temp the motor would start to break. I'd guess it's less than 92degC and also dependent on the type of driving the car does.
A majority of my driving is on the highway, that's where I heard a warmer motor does best. I'd figure that if it was mostly rush hour or the 'burbs I'd go with a cooler thermostat to get the car up to temp as quickly as possible.