Honestly, with how awesome the new 1-60 is and how grindy Outland and Northrend are, I wouldn't mind changing the heirlooms to "Decreases XP gains from 1-60 by 10%, increases XP gains from 60-80 by 50%, increases XP gains from 80-85 by 10%". The new stuff goes by way too fast and the old stuff still takes FOREVER. Even in a full set of heirlooms, 60-80 seems to drag on for a lifetime.