Have you used Financial Engines to model retirement? I get access to the service through Vanguard. I believe many 401k plans offer the service as well. It is pretty detailed, and it pulls in all actual account values.
As part of my final tests before FIRE, I took a look again. In the past, it has shown me to be on a glide path to retirement. It previously predicted 95+% chance of success, assuming all the numbers remain true. This time it projected a wildly optimistic spending rate of over 6% of current assets. I did plug in projected social security payments, and told it to start in 10 years, my full retirement age. SSA will pay about 2% of future assets when it kicks in.
I will use a few more tools and people for review before I FIRE, and pick 2nd worst result or similar. Curious about other folks experience with FE.