I am in a similar situation to the OP and have been enrolled in the PAYE plan for over two years. I sent most of the following to the OP in a PM, but I think it would add to the dialogue.
A few thoughts:
1) I 100% completely support the OP's plan. I think the math checks out and it is clearly in your best interest. I've been pushing you toward this on every thread we've both been on.
2) It seems that most (all?) of the critiques are people who are advancing some kind of moral argument. The OP knows where I stand on this and even quoted me in the thread. It's a business decision and the terms are spelled out in the contract. I don't see any type of moral component whatsoever.
Moreover, to this point, I think IBR programs actually work out in the government's favor. PSLF is obviously a good outcome because it allows highly qualified workers to take lower paying jobs. Certainly I think the government comes out ahead there. But a greater point is people like you and I. We are in somewhat similar situations and I fully expect that we will benefit from the IBR programs by paying less money back and over a longer period of time. What people do not consider is that our incomes and therefore our income taxes are so much higher because we took out student loans. If it weren't for law and MBA school, I'd probably be making 40k a year or less. Now I'm 6 figures and the sky is the limit ... all the while these taxes are going to uncle sam. Remember, it all goes to the same place.
Lastly, how is using this program to your benefit any different than using a Roth Ladder or other estate planning mechanism to minimize taxes? There's no moral issue here... its simply people being rational and optimizing their net worth under the current rules.
3) Keep in mind that PAYE and IBR is pretty nuanced stuff with a lot of detail. I don't think most of the posters on this thread are familiar with the details of the program... why would they be unless they had $$$ loans. Like most things, the devil (or in this case, the benefits) are in the details. For someone who graduates college with a liberal arts or other non-marketable degree, in my opinion, Grad School + IBR/PAYE/REPAYE etc is the surest way to FIRE if used correctly.
4) Some people think these programs give you an incentive not to make the most money possible. Totally incorrect. You know this, but as long as you're paying a % of income, you should always try to make as much as you can. At the end of the day you still keep $0.90 of every $1.00 you earn.
5) Being chained to the whims of the government issue -- I suppose this could be a concern. Although we do have a contract spelling out the terms of PAYE and I've been making payments under this contract for over two years, so I don't think, legally speaking, it could be amended at this point. I also remember that congress is a bunch of elected officials (and millennials are now the largest population group) so I cannot imagine any scenario where they would take benefits away from so many people using the program. I recently read a stat about the number of people using IBR programs.. I can't find it now, but it is shockingly high.
6) Tax issue. Yes, this is definitely a concern and a drawback. However, I do believe that there is a better than 50% chance the law changes and the forgiven amount is nontaxable. That said, I'm preparing for the worst and just budgeting for the tax bill. $100,000 due in 20 years really isn't that difficult to save for. And considering time value of money, that is much much less than $100,000 in real dollars today. Considering all the benefits of IBR and the amount you will be able to save because of it, this drawback is really kind of minor. Also, (and admittedly I have not even scratched the surface of researching this), I bet there are some estate planning techniques that one can use to move assets around and become insolvent when the tax bill comes.
In summary, I think your plan is a good one and the numbers check out. It is difficult to project your income for the next 25 years and it is very possible that you will end up paying more money back under REPAYE. However, if you do, that means you made A LOT of money over that time period. That is a good outcome. The goal is not to somehow beat the government into paying less, the goal is FIRE and this is a tool to get you there. If you manage to wind up paying more back under the program you will also have millions of dollars saved, that is a WIN. The program is also a tremendous hedge. If you die or become disabled, your loans are extinguished but your savings and retirement accounts are not. If you become unemployed, your student loans go to $0, while your bank accounts remain intact. Literally the worst thing that can happen to you with this plan is that you make too much money... what a nice problem to have.
Good luck.
-Tank