Your cadence must be quite slow. I can hit between 25-28mph with a compact front (on big ring) and an 11-32t rear but still have 3 or 4 cogs to go. I run out of power before I run out of gears (i.e. I hit the point where changing up slows me down rather than speeds me up)
EDIT: meant to add that my cadence is in the mid 90's to low 100's at that point.