I am thinking about switching to a shorter stem for my CAAD8; from 100mm to 90mm. My LBS sung me the praises of Thomson stems and sold me an X4 for $90. When I looked it up on the internet, I find out that the X4 is the mountain bike stem and the X2 is the road bike stem. He sold me the wrong stem!

I might as well order online if my LBS manager can't properly sell me the right kind of stem, at a premium price. Question, does the name brand of the stem really matter? If so, what would you recommend?

thanks