70% highest bracket starting at $500,000. Plus 50% bracket from $200,000 to $500,000. No changes in brackets under $200,000
I think that's about right. I would however caution the notion that there's a magic formula, which there is not. Back in the days when our elected representatives considered that paying for stuff was doing the work of the people (post WWII), including Republicans, and thus the debt was paid down, they tinkered with nearly every bracket, almost every year, fine tuning revenue targets while not slowing growth. It worked, quite well.
So the best answer, in my opinon, is of course raise it; we need more revenue if we hope to pay off the Trickledown/Supplyside debt in a post-Failed Rightwing Policies era. But then see what the effect is. If revenue is not sufficient, and growth continues upwardly, raise some or all of the brackets some more, until we reach a point of diminsihing return. Get 'er done