yes, the graphite chassis will crack if you race them on todays big jumps tracks. if you even case the jumps a few times, your chassis will snap. i now use OT-122 alloy chassis and have no worries at all. See my blog for more info.
http://superturbooptimamidspecialzx-5.blogspot.com/
keep in mind after a few months of hard pounding, i managed to partially snap a Lazer front arm, and also bent the RCPS titanium hingepin. This wouldnt have haapened if i cleared the big jump at the track, but my 10.5 did not give me enough speed at times to clear it. i magine slapping into the other jump from maximum height, either on the chassis or the front bumper or the front arms.. thats what happened to my Mid, that snapped my arm. Not only that , i also shook the motor plate loose, becuase of the jolt stripped the thread in the top deck mount near the motor, causing the spur and pinion mech to go off and destroy the spur. i have since rebuilt the front suspension with MPP lazer arms, since i got 8 bags of them. i am now in the process of getting a new brushless ESC + 8.5T motor combo so that i will have more speed to clear the jumps and land properly to avoid destroying the car. Dont get me wrong, the Optima Mid is still wayy tougher than todays cars, but if they get abuse constantly soemthing will eventually give as in my case. i surmise since with the more powerful 8.5T i will slam the car a lot less. i am only slamming the car badly at the big jumps anyway.