Mine went early this year too. I pulled half and left half ... the ones in the ground didn't seem to get any bigger as the leaves dried down. The only thing I don't know is if harvesting before they are brown will affect the storage quality but I doubt it - if I pull them when there is still green I cure them on a screen so it seems that doing the same in the ground wouldn't make much difference.

I'm growing Leeks for the first time and read that they should be given a hair cut to keep them upright. I cut them last week and they are looking good.