I would ask what other tasks you intend to use this file for? Is this a one time delete?

I would hazard a guess that this file has a purpose outside of storing a bunch of serials that are only to be deleted from ;-)! Will someone be adding to this list, making changes, looking up entries in it? On a regular basis?

I would tend to lean DB for anything like this (though not everything).

May I suggest that before you take any further action (unless the need is immediate), you analyze what else you may do with this data. You might find the best answer for this problem in the general use of the data itself.

-digiryde