What the spreadsheet tells us is that you will have better than 2.5% accuracy if you:

• round to the nearest hundred sats/$whenbitcoinisbetween4000and2100sats/$ ($25ktoabout$48k)
• round to the nearest fifty sats/$whenbitcoinisbetween2100and1000sats/$ (about $50kto$100k)

Another way to put it is "above 2100 sats/$,roundtonearest100,below2100sats/$ round to nearest 50."

This works up to $100k/BTC