Internationally, mandatory-language design standards – ASCE 74 and CEN/TS 19101 – address the structural design of pultruded GFRP structures. While member capacity determination in both standards is founded on anisotropic plate theory, assumptions made in each standard result in potentially very different capacity calculations for typical pultruded GFRP members. Complicating this, ASCE 74 departs significantly from earlier available design guidance upon which it is based. In this paper, it is shown, depending on the standard applied and assumptions made, that some structural designs may be excessively conservative (i.e., over designed and inefficient), while others may not achieve the reliability intended by the standard. This study investigates the implications of equation selection on flexure-induced local buckling capacities of common pultruded GFRP cross sections (I, W, C, square and rectangular shapes) and the implications of adopting the simplifying assumption of simply-supported flange and web boundaries. The effect of the flange boundary assumptions is shown to potentially have a significant impact on member structural efficiency.