The Great Pyrenees I see seem to really slow down by the time they are six years old. That gives only about four years of reliability once the 2 years of maturation are taken into account. We have some Akbash running about they seem to age much better are much more athletic and able to do rounds at higher temperatures.Well their dogs were obviously in great condition. Running around with no arthritis at 8 years old.
If you get a good line, they aren't any slower than say a Great Pyr or a Maremma. Both of those breeds have a life expectancy of 10-11 years.