Most of the Buicks in their fleet have the same Supercharged V6 as the Pontiac Grand Prix. So if you think they're having trouble reaching speed limits, you're on something. And considering most of them share most of the suspension work from the Grand Prix and Bonneville, then you'd know that they handle nearly as well. And no, their brakes and steering are not faulty either.
I've worked at a Buick dealership and I drove these vehicles on a daily basis. There's nothing wrong with the cars themselves, especially for the group they cater to.
Saturn is no longer unique, however due to that they're also the least likely to be killed off by GM. GM has poured a lot of money into Saturn and is trying to turn them into an upscale brand, in fact almost on par with Buick.