Depending on the grade of the stud.....preferably something less than what the strap clamps and T-slot can handle? I've seen both fail, but replacment T-slots are not listed in any catalog . If clamps won't hold it down solid, then reducing the load is better than breaking things trying to hold it tighter.
Bolt clamping loads
Since the clamping point is offset from the stud; the clamping forces at the part being held can be greatly effected by the fulcrum point of the stud to the part, the area the clamp is contacting on the part and the distance to the support at the other end of the strap clamp. It would be easier to relate this to a percentage of the X lbs of force rather than a direct PSI holding the part down.
Looking at the chart linked above for 1/2-13, it is realistic to put near 10,000 lbs of clamping force at the stud with around 75-90ft-lbs of torque. I'd gather the strap clamp won't handle that much, but one could take a SWAG at some of the lower torque data listed there and be close enough.