I spent 13 years in the IAI 1125 ASTRA and it was a 0.78 cruiser with 0.835 MMO. Is the SPx different?
Absolutely. It's a completely different bird.
From the QRH, max cruise:
FL450, ISA, 17000 lbs, 0.81, ISA - 10 gives 0.835, ISA + 10 gives 0.717
FL370, ISA, 24000 lbs, 0.825
FL390, ISA, 16000 lbs, 0.839
FL410, ISA, 18000 lbs, 0.83, ISA - 10 gives 0.847
Mmo 0.875
Vmo 353 KTS
High speed climb is 0.72