What is special/different about CyanogenMod's kernel? (especially compared to. DroidX GB kernel)
CyanogenMod is a tweaked kernel. Because of this it's faster, since the team that make it work pretty hard to make Android more faster and stable as possible and also it's already rooted, so you don't need to go all over the process of rooting again.

I highly recommend you to check the CyanogenMod Wiki