i do a lot of this stuff and all the agencies want nice small files.. some want between 1-3 meg.. a BIG angency i submit to say any bigger than 2 meg is OVERKILL!!!
you want to be just under 1 meg.. that'll fill any national paper with a good print.. as good as it'll get in a paper anyway..
Jpg compressed to about 4-5 will do.
Hope this helps..