Mountain bike for adventure races

Hello! I am a long time runner and would like to begin doing adventure races. I have been trying to research bikes and I think the main thing I have learned is make sure it fits. However the whole, which bike is better for what activity and which parts are best is very overwhelming. Two bikes have been suggested to me by two different people. Bike One: Gary Fisher, Mariln Disc GS and bike two: Specialized Myka Comp. Can anyone help me by giving their opinion on if the Gary Fisher is worth the extra $150 over the Specialized? Or does anyone have suggestions of other bikes? Since I am new, I am trying not to spend a huge amount until I know for sure this is something I will really enjoy and continue to do. Thank you for your help.

educate yourself about mountain bike fit ( there are some good threads you can search for) and then buy the one that fits best. Fit is one of the most important factors in a mountain bike purchase.

Be sure to try a 29er or two and make sure you don't like them better than 26" wheeled bikes!