On the brochure, GS's curb weight is 2,204 kgs and gross weight is 2,770 kgs.
With these load indices:
Load Index Chart
So, parked it's 2,204 kgs / 4 tires is 551 kg per tire. So at the very least the tire should have a Load index of 88 (560 kgs).
Say you usually have a driver and a passenger weighing about 150 lbs each (136 kg total), then it's 2,340 kgs or 585 kg per tire. At least 90 load index.
If you have a total of 9 occupants at say 150 lbs average (614 kg total), it's about 705 kg per tire or at least 96 load index.
I agree with fast lane, 102 should be safe enough even if loaded. For my 18s, I had been on 235/50 with a 97 load index for over 2.5 years. Sure it wasn't fully laden most of the time -- average of 2,400 kgs half of the time, or much less for others. Treadwear was the issue for the tire change though. I'm now using 101 load index on 235/50r18.