Monster stocks tend to tap into long-lived trends that support growth in their markets, and they typically do so using evergreen business models that don't change much over time. With that in mind, here are two monster growth stocks that are likely to keep performing strongly whether you're investing for three years or for 30 -- and both are ripe for purchase right now. Without Steris, (NYSE: STE), you probably wouldn't find the cleanliness standards of your local hospital to be up to snuff, as it's one of the most crucial suppliers of sterilization products and services for the entire healthcare sector.