145 is 99.9th %ile. Performance at +3 SDs is so rare that a very small percentile change represents a fairly sizable standard score difference. Beyond +2 SD (130), we are talking about way out on the tail of the bell curve. Providing some perspective, remember that "only" around 130 is still quite low incidence, and substantially above average performance.
Also, achievement scores may or may not fully capture even a PG child's full range, as there are other factors (such as exposure to/instruction in certain topics or skills) as well. The achievement scores you posted could very well be consistent with PG-level cognitive ability (though they could also be consistent with MG or HG-level cognition). In particular, the WIAT-III reading comprehension subtest has quite a low ceiling (for HG+ purposes), due to the item set structure. Similarly the oral reading fluency subtest, with the added impact of rote speed (which is usually not as exceptional in HG+ children as their reasoning skills are).
