The trails have the servo wave lever system which has a non linear pull. The races don't have the servo wave so the pull is linear. With the race the amount you pull on the lever is the amount the calipers squeeze. With the trails, for the first bit of pull it is linear, then the servo wave kicks in and pull becomes non linear. The calipers squeeze faster than the lever is pulling, giving, according to Shimano, more power. It is a very different lever feel and takes a little getting used to, but I really like them.
The trails are essentially the same as the XTs minus about 30 grams so unless you're a weight weenie I'd spend the extra money elsewhere and get the XTs.