The formula for Action Points seems to be wrong (currently listed as "+0.4 Turn Action Points per point (base 4)"). From my testing, it seems so far that the SPD bonus is calculated as (SPD - 1) / 2, rounded down. That rounded integer SPD bonus is then what factors into things like the x2 Glass Cannon AP calculations, done post-rounding.
While the formula above is the correct one, I edited the info here using a much simpler method of calculating Turn Action Points, which is 0.5 per point in Speed, and the base number being 3.5. I calculated Turn Action Points with both methods and the outcomes are always exactly the same. - SunnyGrim