If it is to harm him and make the rest of the world satisfied with it 25 years behind bars seems enough to me, I don’t care if it is 25, 35 or 155. In five years I will have forgotten about this.
If it is stopping others, same thing, I don’t think that if someone is determined to do something similar would care about 25 or more years.
Then it’s to stop other bright minds from attempting anything like this - they’ll remember SBF. His crime has a price now: 20-25 years
Sincerely
The American Legal System
Obviously there is a sweet spot. For example, if you're okay with 60 years, than you're probably okay with 80. I'd imagine 20, give or take 5 years or so, is near that sweet spot, but that's just my gut feeling. Obviously statistics is key here, if there is any.