Thank you BSA and Genuine_S for the wealth of information.
I will only upgrade one SD to 18" wheels. It will be for long distances hence the need for larger wheels to cover more distance. I will also fit it with Brooks Flyer since longer distances means longer time sitting upright so a sprung saddle is needed. This will be like my “race-bred” or “touring” Strida.
My original SD will be my everyday commute bike. Since my route is fairly short with some minor climbs.
Different bike for different purpose.