I hate pace predictors.
According to Macmillan, a 33:15 5K (that's about a 10:45 min/mile pace) like I ran today will only buy me a 5:24 marathon finish time (~12:20 min/mile).
That just sucks.
But so do those last 6 miles of the marathon. . . .
And it's still an improvement on the 5:26-equivalent I ran just a few days ago, too. It's still moving in the correct direction.