More practice would be better for Calabogie. Like Peter said, the track is highly technical, difficult, and has 20 something turns. The other point being Calabogie doesn't have the luxury of great run off, so when it goes bad it could get really bad. We should remember that Armco was positioned as it is to corral cars, and it isn't bike friendly.
I am specfically thinking at the exit of turn 4 and specifcally Big Rock (turn 6), off camber, down hill, left turn - Armco track side.
Exit of Temptation (turn Armco 15 ft off race line at exit. If you lose it you hit the Armco, if you panic and lock the front you fall and take out the following riders.
Deliverance (turn 9) Armco at track side left.
Turn 12B , lots of high sides here.
Turn 16, left into the gravel pit,... front goes light or wheelies, just as you turn.
Wilsons (turn 20) on the front straight.
Turn 1, if it goes wrong at speed you are right into the Armco.
Anyways you get the idea. Most of us mere mortals require 2 full track days to figure out which way the corners go, and how to get relatively fast safely. I tend to do the odd Pro6 day and the DOCC rally's at the track. Having worked the crash truck I can say that when it goes bad at Calabogie it can be very bad.
So I would rather have more practice than a 3 hour Endurance Race.
That's my 2 cents.