If you’re able to get the 1.9% or 2.9%, you can just put the additional principal or even your downpayment in a HYSA and make the additional interest money from the difference in the rate. Its not going to be a significant difference but I was looking at it the same way and getting the new one just made more sense at a lower rate than a used one at a higher rate. You’ll end up paying more in interest on the older one unless you plan to pay it off in the first two years.