You can back test it if you like. .. but you have to start with the right premises and valuating your stash based on the 200-WMA in terms of figuring out your budget, and right now 20 BTC is ONLY worth $663k according to the 200-WMa, and 5 years ago, you would have had needed 191 BTC to be at the equivalent 200WMA valuation, and so if you had spent 191 BTC at 10% per year, right now you would still have around 75.3 BTC, so you would have had kept your value by spending 10% per year, and if you had done the max 10% withdrawal for that whole time, you would have had withdrawn close to $2 million in value during that time... and your remaining stash BTC would be even more valuable (in terms of dollars) than they were when you started.
When I looked at the past data I came up taking 20-25% in a bull year for 4yr future period. So sort of in that 4-6%/yr range. The main reason I went this way is because of the variance in % withdrawal required when you do it annually(or monthly etc) You could end up withdrawing more, like closer to 8-9%/yr. I’m still playing around with my data tho. Stash size is a consideration for sure though ;-)