Quality of the list (is it clean? ... what is the ratio of 'freebie seekers' to truly interested participants?), relationship (this can make a list of 5,000 pull better than one of 100,000), how targeted the offers are to the basic need of the list, and how enticing the offer is beyond that are all variables to how successful a list can be.
I actually had a sub list of only a little over 200 that was targeted to those interested in the release of one high ticket product ... I made 22 sales when that product was released. I offered a $250 rebate as a draw for a $997 product, so I walked away with over $5000 in commissions from a list only 2 months old that I promoted to only a handful of times ... and it continues to grow on auto pilot for the follow up to that high ticket product.
Guess what I'm trying to say is size doesn't really matter, unless you're going to hold yourself to one general list ... and even then, relationship and list maintenance (quality) out ranks size in comparison.