No worries Cliff, I appreciate your reply.
I usually shoot wide open unless I'm going for the panning effect, where I will use shutter priority. Probably 90% of my MX shots are taken wide open.
Mostly these are the reasons:
1. Background blur. Distracting objects and people are found all over the track.
2. Stopping the action. I have yet to come across a situation where it's so bright outside, that the shutter speed is so high the wheels are frozen.
3. I didn't pay all that money for the 300/2.8 only to use it at f/22. 
4. Right now I like nice tight MX shots, as I start stepping back a little bit and shoot other aspects of the race, I will definitely stop down some.
Happy shooting!