If you send a single email to each person on your list and don't email them again unless they request more information or signup to your news list, then I don't think it matters how big your list is, the only question that comes to mind is if your list is too big, it reduces the odds that its well targeted?

I guess it depends who the target market are, and how big it is. In my business id probably hand pick the companies on my list.

Its not to businesses but consumers...