Had to choose between a big email list or a small one that really wanted our stuff

We were launching a new tool and had two lists: one with 50,000 old sign-ups and one with 2,000 people who clicked a specific ad. I sent the launch email to the small list first. The open rate was 38% and we got 80 sales in a day. The big list only got a 4% open rate when we tried it later. Do you think focusing on smaller, warmer groups is always better than going for a big, cold audience first?