speed and/or horsepower have nothing to do with the turbos going. on our new volvos at my company the turbos go out at about 250k -300k. it's just the oil seals or chamber seals wearing out and failing. as long as the wastegate actuator is working properly and there is oil flowing over the journals, it doesn't matter if it's on a 50 or 500 hp motor.
if you want to extend the life of your turbo, let the truck idle for about a minute before shutting it off. it lets the turbo and the oil flowing through it cool down. if you cut it off immediately a crust of oil forms and causes premature wear. this is the reason why people with big HP turbo'd street cars use a device called a turbo timer.