The Beast doesn't go 80 mph and the old trains were A LOT heavier then PTC's.
http://www.premier-r...stallations.htm
For the old premier trains...
The PTC's that The Beast use are around 900 per coach. No I don't have a link. I was told by a engineer I know that has worked with PTC trains.
Round that up you get about 5,400 pounds for a train. Take the old premier and you get about 16,000 per train. If you don't believe me do the math.
And the problems with Son of Beast now really don't have to do with the structure as much as it did. The trains they have now were not designed to fit the track gauge Son of Beast has. The trains were heavily modified. That's why the ride is still rough.
And for Intimidator I305 I haven't read anything from the park about the trims added to the first drop. But I did hear the ride was destroying wheels and only one train was being ran most of the time because of them constantly removing and replacing wheels. Not sure if that is entirely true though. And yes I know about people almost blacking out on the ride.