Nancy,
I tried a couple of things. One I modified the code so that there was no reference to .NewItemID inside the loop using a memvar instead. The results there were similar to the original although the AddListItem was a little beter.
The important thing I noticed is based on my second test. I tried reducing the number of items being added from 1000, to 500, and then 200. With each reduction the difference between the two methods got smaller until, at 200 items, they were .01 seconds different.