Upload & Sell: On
If your objective was shooting "motion blur" MX photos using 160th of a second exposure at a focal length between 61 and 70mm I guess you accomplished your goals.
I don't mean to come off to harsh but to me all but the first photo are nothing more than motion blur snapshoots, which suffer mostly due to very "busy" backgorunds, but like you said you were trying out your new camera and I'll cut you some slack.
If you want to learn the most effective way to shoot sports images that have impact, which translates into more "sellable" images, watch the following video / interview with Getty photogapher Adam Pretty from last summer's Olympics.
What you'll learn from the video is to start thinking in reverse, in this order "interesting background, interesting lighting and finally interesting subject."
Regardless of what your subject is, or what shutter speed or aperture you choose, you need to be in control of the backgounds if you want you photos to stand out.
Hope this helps.