Makes sense to me. I had a similar idea when I saw a report on chain line efficiency. The other bit of info you need to take into account is cadence. Without that lots of ratios will get you to any speed but you want the ratio with the best line at your comfortable cadence. What I would do is cruise around a bit at your 27mph then decide which gear ratio you prefer at that speed. Then it’s just using a gear calculator to replicate that ratio at a chosen place on the cassette. Get that ratio on your current set up and then comeback to double check the maths.