Ron, the Alpine studs are also 7/16-20 and the manual specifies 48 ft-lb. I have heard that over-torquing could stretch the studs, weakening them. I think this could also lead to thinning at the root where the stud grips the axle plate, so that may explain your experience.
I have a table that shows the torque for dry threads on a 7/16-20 bolt at 55 ft-lb for grade 5 and 80 ft-lb for grade 8. Another website I saw calls out 41 and 58 ft-lb (with tension at 70% of yield), logically then higher torque puts the stud closer to yield, but I don’t know how to figure how much. I don’t know what grade the studs used by Rootes may be, but I doubt that they are grade 8.
You might want to consider a stronger stud material if you can find it. I could be wrong, but I think the critical item is the clamping force, so as long as the spacer used is incompressible, the longer stud shouldn’t change that.
FWIW my Z4 is specified at 130 nm or 96 ft-lb.
I’m sure there’s a mechanical engineer out there that can chime in on this topic with a better discussion of wheel stud torque, clamping force and the impact of axle torque on the studs. I’d like to learn a bit more too.