I've got Apex, One, and Sport and they have similar variability from nominal.
owfinc.com specs it, for example, 1/2 to 1 inch loft. They said it varies from place to place on the batt, and from batch to batch.
I think if you got 4.45 oz instead of the nominal 5 oz, it will be proportionally less warm.
On the other hand, it would be difficult for you to tell the difference between two garments - 4.45 and 5 oz.