I haven't had any trouble with mine. Tons of 12 second passes and a few high 11's.
After that you should get a 'cage anyway. The 'cage will not allow the chassis to flex as much if done correctly.
I have seen some VERY fast stage II cars with a cage and T-tops - One of them glued them in though as they tend to pull up at high (150+) MPH.
HTH