My humble opinion is that stock drive shafts are highly variable. I have at least 50 passes with slicks on my bone stock shaft and U-joints, with some 60-foot times in the 1.6's. A friend in my club broke his shaft near the finish line one day and put a hole through his floor board on a high-11 second car that didn't have many passes on it. I think there is a lot of variability shaft to shaft, and any wear, dents, or abuse put on the shaft by previous owners definitely comes into play.
Before I go back to the track, I'm planning to upgrade mine to be safe.
Sent from my SCH-I535 using Turbo Buick