In my experience, Monte Carlo-based simulators will be more conservative than firecalc by about 1% on the WR. So if firecalc says you are safe at 4%, a Monte Carlo simulator will say you're safe at 3%. Roughly speaking and YMMV.
"At times the world can seem an unfriendly and sinister place, but believe us when we say there is much more good in it than bad. All you have to do is look hard enough, and what might seem to be a series of unfortunate events, may in fact be the first steps of a journey." Violet Baudelaire.