See above in red or if easier, point me to the thread that dives further into this?
Overall, interesting approach. I'm not sure I have the risk tolerance on my core portfolio you have, but definitely have been thinking about letting the excess run 100% equities. My WR is running between 2% - 2.5% and is a relatively large planned spend which is extremely discretionary fat-filled and grows annually. Realistically, short of big annual gifts to the kids, I don't see myself spending at this rate until the dirt nap, but planning none the less.
I don't think I have a thread for it anywhere. I just spell it out periodically if it seems relevant.
I clipped out your red stuff out and putting it in quotes so you can see what I'm replying to - hopefully that's OK:
1. "Do you run a basic all inclusive needs/wants/wishes annual spend, or just a general needs spend? In other words, do you include projected lumpy expenses and gifting or does that come out of the legacy bucket?" For my base FIREcalc run, I use my recent actual spending, so it's everything I've spent in Quicken the last six months multiplied by 2 to make it annual. I do subtract out the "College" category because that comes from a separate dedicated bucket of funds.
I lead a fairly boring life so I don't really have large lumpy expenses. I actually and somewhat uncharacteristically handwave at any analysis there and rely on having a 1% WR 99% of the time to cover the potential of those occurring.
2. "Do you mean you plug in your actual planned spend here which gives you the 90/10 at 95%?" No, if I use my actual spend, I get 100% success with any AA. The idea here is if I went hog wild and started spending a lot more, there would be a point where my spending would pass the point of 100% safety at all AAs and enter a region where the safety of my spending would depend on my AA before entering a region where my spending would be unsafe regardless of AA. So I arbitrarily chose a 95% safe spending amount (which would be at the lower end of that middle region). That way I could see how the variation in AA impacted my safety. I then wanted the safest point (which is the "mountain top") on that AA / safety curve. Which, for my particular set of actual inputs but with a single change to my spending to be slightly unsafe, ends up at about a 90/10 AA.
3. "So I read this as you are underwriting effectively the 4% rule at age 53, which you are comfortable to ride at 90/10?" I'm comfortable as long as I'm spending less than 4% of my portfolio at age 53, yes. Since I'm spending approximately 1% of my portfolio, I think my AA really doesn't matter. If I were to spend more to an a marginally unsafe degree, I would want my AA to be the most survivable one at that higher spending level, which turns out to be 90/10 as described above.
4. "I have thought about something similar here where excess is left to run as probable kid inheritance, but I suppose my logic has been the core portfolio (your 25X) should be a more conservative 60/40-ish AA." I agree that the core portfolio should be the most conservative, but I interpret conservative to be the most historically safe WR given the planning horizon.
Somewhat counterintuitively, with a 37 year planning horizon (and my other inputs), historically a 60/40-ish AA is less historically safe than a 90/10 portfolio. At least according to FIREcalc with my inputs. I think it's because 40% bonds is more susceptible to inflation risk than the 60% stocks are to sequence of returns risk, basically.
5. "I'm assuming your 1% - 2% WR is based on your entire portfolio?" Well on my FIRE stash, yes. Which as is typical, excludes my home and possessions, and also excludes my kids' college funds and a potential inheritance. When I calculate that WR number, it does include the NPV of a derated amount of my SS.
I should add that I do my numbers two different ways - one way is via FIREcalc, and the other way is via my homebrew all-purpose Excel spreadsheet. Depending on context this may be a bit confusing. For my WR%, I rely on a calculation in my Excel spreadsheet because it's just a static snapshot based on current balances, current spending (well, last six months in Quicken annualized), and SS estimates and projections.