I had a '04 Bonneville GXP and the hubs went at 42,000 miles and 70,000 miles. I put in the Timkens as they were a far better product than the ACDelcos that were replaced. Never had any trouble afterwards, sold the car with 125,000 and they were tight. I ran the hell out of that car too. Pretty much everyone on pontiacbonnevilleclub recommends Timken.
BTW the Timkens are under $110 on RockAuto. Here in town at the local parts place, $348. The Motorcrafts are cheaper at the dealership than the Timkens anywhere locally. Very good product. Stay away from the Moogs, unless you enjoy doing hubs.