WIth the subtle approach I tried lots of combinations. Here's what took the most cash.
Cheapest driver works fine.
Packie as the gunman (found in a random event south of Franklin's house). Cheapest one drops a large portion of the take.
Rickie (available after the Life Invader mission)as hacker. Only takes 4% but gives you enough time to empty the store.
Overall Michael took just over $1.2 million.
And Franklin took $29,000.
Thats the best I could do. I didnt have Taliana Martinez, another crew member you can recruit from a world encounter, but doubt she would take less than an 8% cut anyway.
So thats the best I could do, enjoy.