It looks like you are putting lots of effort into planning, but the tool you discussed was FICalc which is more of a high level tool. If you want to get more specific and include the effect of taxes, I suggest trying Pralana. It has great flexibility and power and supports Guyton-Klinger as well as other variable withdrawal strategies like Actuarial and Consumption Smoothing.My calculations are for Guyton Klinger using a starting WR of $105,000.00 (so approx 4.6% of my starting balance) and then I have to calculate every year based on market performance. My WR can go up or down if things are good or bad. With this approach I am able to put in $90,000.00 as my minimum spending (if you don't do this GK always reaches 100% because it will just adjust your spending down to whatever is needed to make the plan succeed). So I have already figured in my minimum ($90,000.00 in 2027 dollars) so I should never have to adjust below that. If the market tanks enough to get me to $90,000.00 I keep that until it corrects, that is the lowest I have told the calculator I am willing to go. That all said I can realistically cut way down from that if I really needed to.
In Pralana's Guyton-Klinger implementation, it takes care of the spending floor issue by using all your listed expenses as essential and varying your discretionary spending. The program has historical and Monte Carlo analysis in addition to deterministic modeling. One feature I like in historical modeling is you can choose a particular historical start year and see what would have happened, year-by-year, account-by-account using your plan. It's a nice way to really stress test whether you are comfortable with your plan.
Pralana can help optimize Roth Conversions while taking into account ACA. It can't automatically find the exact mix of Roth and Taxable to spend each year, but allows you to test that manually and it has an optimizer that tests which account to use first, testing 625 combinations (total) across up to three time periods. Of course it also has a tool that projects your earliest safe retirement date.