Text (5th+errata): If target creature has toughness 5 or greater, it gets +4/-4 until end of turn. Otherwise, it gets +4/-X until end of turn, where X is its toughness minus 1. [Oracle 2005/08/01]
The check against toughness to decide if it applies +4/-4 or calculates a value for X is done during resolution. This decision and the value of X (if appropriate) is locked in on resolution and is not recalculated. [D'Angelo 2005/12/01]
