Unfortunately, most shows don't weigh birds. The SOP guidelines are there as a reference so breeders can have a goal. Birds do not have to be that exact weight to be winners. Also, in a dual purpose bird that was primarily, traditionally used as a table bird, points are not deducted for being over SOP weight unless they are substantially oversized to the point that they do not represent the breed well. The specific excesses that are allowed without deduction are listed in the SOP (check that important front part of the book, not just the specific breed descriptions), but if memory serves me well there is no deduction for up to one pound over the listed weight, and after that there is only a small deduction for every half pound oversized. Obviously, being over the listed weight but in excellent body condition is different than being an overweight (i.e., fat) bird, as a bird that has an extra pound of fat would hopefully be judged as a poor specimen.
If you're interested in showing, I would definitely show those Speckled Sussex without concern about their size. At 5 1/2 months, these are robust birds that appear to represent the breed well. Even if they don't win, you should be proud of them.