Late, but this is slightly off; the cap is 255/256 in both the handheld games and Stadium. Stadium also uses a different formula for Focus Energy that isn't a direct multiplier.High critical hit-ratio moves have a chance of (user's base speed / 64) to crit, capped at 63/64.
in Stadium, it works properly and now quadruples the user's crit rate, capped at 127/128