Agreed. One look around the red pen (sub 4 target I think) will tell you straight away that half the people in there have been optimistic (and some wildly) in their finishing times. Haven't looked at this year's spread, but 4 hours would normally get you into the top third of the field or...
Don't worry, they use your finishing estimate to work out your start pen. You'll probably be in the red one (first of the non-elites) with a 4 hr estimate.