Is that 30.5" from your pubic bone to the floor? That seems pretty short for someone 5' 9" tall. I'm less than 5' 7" and my biking inseam is 30.5", and my legs are relatively short for my height..
If your measurement is correct, I'd go for the 54 and negotiate for shorter crank arms and a much longer stem. I ride a 54 x 56 and use a 110 mm stem. If your legs are my size, you probably could use a stem in the 130-150 mm range. Maybe even longer.