Wide neck version of NAC6 (NAC6A) is the successor to our popular BM100 skimmer. Thanks to a newly redesinged meshwheel, NAC6 is quieter and pulls more air than previous generations.
Either one will be able to handle your 45g with ease.
Actually I think the NAC6A is the newer version of the NAC6 with a wider neck and meshwheel impeller. I dont think they even sell the NAC6 anymore anyway.