I think it's actually due to more people in the chat room. The traffic this weekend was pretty big but it wasn't quite as big as the first weekend X&Y were released, and the site was pretty good that weekend (surprisingly).
The main part of the site is heavily cached so we could have a million visitors and the pages should hold up okay. Pokebase is very "dynamic" so it uses a bit more server resources. When the site was going slow for me on Saturday I went to the chat room and there were over 35 people in there. There are about 15 people in there now, we never had that many on a weekday morning before.