Sorry, but I don’t think anyone’s chance of getting the Johnson is 40%. It is very hard to predict who will get it. I have heard second hand that the essay is very important. My daughter is not a Johnson, but knows a lot of them. She knows very few who applied ED. Assuming your son has a high unweighted gpa and has shown interest, he sounds like he should get in RD, so I’m not sure why you consider RD risky with the profile you have listed.