I trade off between saying each letter and pronouncing it like 'sly as a fox' depending on how lazy I feel. I don't think it matters too much. When you talking about it often it's just more convenient to say sly.
Points go to Mr. AMD for knowing the competition and being first to answer. I wish my motherboard supported SLI, but so far the GTX 670 is doing just fine on it's own for 1080p gaming. Thanks everyone!