Here is one way to find something to compare yourself to that gives you most of the variables you need to do the comparison. Go to connect.garmin.com and search activities. You don't have to have an account to do this. If you search your area first for time trials you can zoom in to the spot on the map where the starting line was and do a search for cycling events. Odds are pretty good that someone had a garmin and uploaded their activity. Sometimes you get lucky and they put a description of the race such as the Cat and their place (if you download the race flyer you can figure out the Cat by looking at the race start times and compare it to the garmin start time).

Then go out and do the same route and compare away. You could get even more detailed by going to wunderground.com and looking up the historical weather data for that day and the time and compare that to the day and time you ride the route.

Here is one I found in less than a minute for a Cat 4/5 time trial. http://connect.garmin.com/activity/86999466