Short of running it yourself, the best way to gauge how tough a course will be is to check the results of past year's races.

The next race on my calander is 7 Sisters, out west in Amherst, Mass., and past year's results suggest that it will live up to its billing as a tough one.  

The race website says as much, describing it so: An out-and-back roller coaster ride along the ridgeline of the Mt. Holyoke Range on a single-track trail.  Very scenic overlooks of the Pioneer Valley with views of the University of Massachusetts, Amherst College, Hampshire College and the Town of Amherst, as well as a beautiful view of the Connecticut River and Northampton to the west.
Extremely hilly with 3,700 feet of climb consisting of many steep hills with hazardous footing in places due to the many sharp basalt rocks that comprise the elevated ridge of Mt. Holyoke.

"Rockhopper" has run 7 Sisters twice, "and loved it," he or she writes on Cool Running's trail runner forum: "It's one of the roughest trail races around. Many, many, very steep climbs/decents (reverse on way back), involving clambering over jagged rocks which are very slippery if wet. Almost no level in the whole thing. That's why it takes someone as good as Ben Nephew almost 2 hours to run only 12 miles."

Looking at results from 2005 and 2006, I see that breaking two hours will get a runner into the top ten. That's a 10-minute mile pace, which many runners would be considered a very slow, easy pace on level terrain. The first-place time last year was 1:42:06 (Paul Low, 32, Mass.), with an astounding 8.5 minute mile pace, and 1:53:52 (Ben Nephew, 29, Mass.) in 2005, for a 9.5 minute mile pace.

The race draws a fairly big field -- well over 200 runners each of the past two years! -- so it must be a fun one... perhaps in that perverse sort of way that counts suffering and difficulty as fun.

In any case, it will be a long day. I figure I will likely take roughly 2.5 to 3 hours to run the course, and it's a two hour drive each way.