Oh cool! Thanks for the info! I was thinking you must of used a pretty fast lens... didn't think about kicking the ISO up so high!
Understandably there are always concerns when you significantly increase the ISO....but that's one of the things you have to do when going after those dark ride shots. When aggressively increasing the ISO, you have to ask yourself 1) how much can I increase the ISO on my camera and still achieve acceptable results? 2) Do I have a program that I can use to get rid of the noise that will inevitably appear at high ISO? To be honest, I simply used Lightroom 4 to minimize noise and I thought it did a pretty good job.