They are pretty tough standard. Mine hasn't broken anything that actually stopped it from running yet, apart from the Titan motor gave out so I lobbed a 12t double in it for a laugh. One area to keep an eye on is the rear bumper, it is very large and an awkward landing can put a big load on the tranny case using the bumper as a lever. I've broken the tranny case but it is holding at the moment. Another problem is the camber blocks. They have a habit of breaking, alloy fixes that if they do though.
Top end standard with a seven cell and 23/86 gearing (which will burn the motor if you use it off road) is about 30 mph. I found it most fun with 20/86 gearing and a 2s lipo, plenty of get up and go, decent top speed and cool running.
The slash will never reach 80mph, the bodyshell is too large, creates too much drag and at above 50mph acts as a big parachute, pulling the truck off the ground. The suspension is also not suitable for high speed, too high and soft. Lowering and stiffening it defeats the object of the slash, mine is slightly lower than usual, but just as soft so it rolls nicely through corners and ducks and dives under braking. If pure speed is what you are after, you want a Bandit or a Rustler VXL.