Basing the below on 2020 data as that's what I had available for now...
Ok, I just researched and found the SLCSP for our area for 2020...it was $1,561.60/mo...or $18,739/year. Per niven, subtracting our premium cap under old law ($66k income x the factor for 4x FPL of 9.5%...not sure how you got 9.83%) = $18,739 - $6,270 = $12,469 which should be our subsidy. So increasing our MAGI by $10k using the new law would cause my new max premium to be 8.5% x $76k, or $6,460....which is an increase of only $190. Is that right?
I guess what confused me initially is the large difference between the cost of the silver plan vs. our current bronze plan. The above shows we'd be paying a bit over $500/mo...yet we are only paying $213/mo for our bronze plan.
If that's the case, then given our much higher cap under this new formula, it seems we would not benefit by purchasing the bronze plan, but would be better off with the better coverage of a silver plan since we're going to pay 8.5% x $76k regardless, right? But can we now change plans for 2020 given that we've already chosen?
It's throwing things off by using 2020 SLCSP numbers instead of 2021, and using 9.5% which is not the percentage your 2021 subsidy would have used for calculation before this change in the law. You could get the correct numbers from healthcare.gov by checking 2021 plans and prices again.
But remember, the subsidy calculated for the SLCSP plan would be the same dollar amount applied to the bronze plan, so you should pay less than 8.5%.
Only you can say whether silver would be better, taking deductibles, cost sharing, etc. into account - we're only talking about the premiums.