I had mine at 27.4 and it was amazing.
I had one @ 25 weeks & my baby was really really clear , although we couldnt find out the gender because my babygirl had her legs crossed .
I scheduled mine for june 5th I'll be 28wks and they told me 28-32wks is the best time to go to see facial features before baby is born. So 27wks isn't far from it (: