While I've done the analysis suggested, the reasons provided above make it a tenuous comparison. I prefer to use the data on page 55 and, with a fair assumption of a normal distribution, project a percentile more granular than just "higher than 99" that's available in the tables.

235 Reading in 3rd grade would be 2.95 SD over mean, or 99.8th percentile among 3rd graders. This comparison against others in-grade seems a bit easier to grasp than some percentile against another grade level.