The upside may be limited here for fundamental reasons.It may sound silly to ask where restaurant company Chipotle Mexican Grill (CMG 2.87%) will be in five years. After all, five years is a long time, and a lot can happen. But making reasonable assumptions about the long term is essential for investors, and five years is a reasonable time frame to consider.According to a 2006 study from Boston Consulting Group, top-line growth, profit-margin improvement, and higher valuations have historically been the thr ...