Regarding shear limit, isn't it the aluminum threads in the stem itself which is most likely to strip?
I have recently upgrade to wider/stiffer bars and have noticed a significant improvement in handling. I thought I would see if a stiffer stem (than my Ritchey WCS 4-Axis) would continue improving things. To save weight I'd like to keep using my Ti bolts as long as it won't reduce the improvements i am seeking.
I have a car. I made a choice. I ride my bike.
As many stem manufacturers point out, not all Ti bolts are rated the same and not all are designed for the torque for a stem face plate. Some stem manufacturers provide expensive Ti bolts on some stems like FSA and Ritchey, but other companies like Race Face warn against replacing the high strength steel (that tend to get a film of surface rust) with Ti bolts, as the cheaper Ti bolts are more inclined to shear where the threads are cut instead of rolled.
The answer is no. At least in my own experience. The strength of four screws is so much greater than the force exerted on them. You could probably crack the stem faceplate by overtorquing them, before they would fail.