I think this becomes more interesting if you're not selling it for fiat and you're just spending the Bitcoin directly, the issue with this calculation is how do you factor in the taxes of going back to fiat

Logic would dictate you start by selling your most recent UTXOs to try and lower your tax obligation but even at its lowest, you're going to be eating into that assumed 20% CAGR and if taxes keep going up and CAGR doesn't trends down, you're selling more bitcoin to get less fiat in some cases

Ofcourse if you really have a massive stack it doesn't matter but very few of us are going to be 50-100 coiners