Hi Midpack, I know you are aware of this and maybe I'm reading this too fast, but FIRECalc's default for inflation is the CPI (not 3% constant). By using CPI one will get the bad post WW2 inflation and especially important, the 1970's inflation that tends to make the retirement start year of 1968 the worst scenario (in modern market times).
Would it perhaps be better to use CPI and independently calculate the inflation adjusted spending level based on known CPI data from the St. Louis Fed? Let me know if you want a link.