The spec for the three nuts that secure the ball joint to lower control arm is 60Nm if the arm is cast steel, but 100Nm is the arm is steel sheet. Can anyone explain this? 100Nm seems like a crazy torque for a M10 thread. I have the pressed sheet steel control arms.

Probably to do with embedding of the nut's mating face (and that of the balljoint if textured) being different on the two types of wishbone, together with the fact that when a fastener is tensioned by torque alone, a very high proportion of that torque is used in overcoming friction, rather than actually extending the screw.

There's a lot of techy stuff about pre-tensioning threaded fasteners, and the general trend towards using a lower torque followed by an angle tightening stage is mostly about reducing the variability impact of this friction.

Ok then. Let's hope the studs are made of some pretty amazing steel to take that torque without snapping.