What's your working weight with S and S? That might matter.
But I don't know what is optimal, I just know what feels good to me. I do my workout with the 32kg, I started doing the goblets with a 24, and after a few weeks I'm using the 32. I do the halos with a 16.
I don't always do halos (they can bother my bad shoulder), but when I do, I use the 16kg. I think the halo is mostly about movement, so the 16kg is probably heavy enough.
I almost always do goblet squats in each session. While they are also mostly about movement (prying), I think there's a degree of benefit from going heavier than the 16kg for them. I'm currently using the 24kg and will probably move up to the 32kg if/when appropriate.
I just see the goblet squat as offering strength benefits for the squat movement, core (chain link), and shoulders. So, it seems appropriate to go heavier than you would with halos.
I have been thinking about that, too. I had been using a 12 for the halos, but recently switched to a 16. Strength wise, the 16 does not seem difficult, but my left shoulder is starting to bother me. I am going to move back down to the 12 for halos and see if that clears it up. I would eventually like to move back to the 16 for halos, but being pain free is more important.
I started off using the 16 for goblet squats, but recently moved up to the 24. This feels good and I will probably stick with this for a while.
I am currently using the 24 for swings and the 32 for getups. My lower back is starting to bother me. It never bothers me during my workout, but will hurt in the morning. I kind of have a feeling that the getups are irritating my back, but it am not sure. I am going to go back down to the 24 for getups for a few days and reevaluate. The 24 seems so easy it doesn't feel like a workout.
If you are actually capable of doing the Sinister workout, I would think that the 48kg goblet squat would be the least of your worries as you are likely to be a serious badass! I would be more worried about creating a hole in the floor, dropping the KB during a get up.