The KD C8 you linked to is the light that got a lot of people started on their flashlight addiction. Do a quick search and you will see one of the original threads on this light - it has to be in the top 10 for most posts on BLF. You can't go wrong with this one and the price is right. As far as the XinTD goes, you probably won't be able to tell much difference in output from the KD, but the quality is better. Keygos are nice, but if you look around on BLF, you will see there has been a lot of variation in quality and output. They do look nice and the price is right. I agree on the 3 modes - I have always hated disco. 
Re: the Brooks. What can I say. Some folks think putting an old leather boat anchor on a modern bike is wrong. You are the only one that can decide that. I rode a Lemond Maiotte Jaune (aka Trek 5900) for years with mine. When you are putting in the miles, who would you rather listen to: Other (misinformed) riders or your ass? If the weight bothers you, go for Ti at much more $$$ or get a smaller Colt, Swift or Swallow. And the Brooks do help with the comfort of the boys, but that is more a matter of proper fit and position. Also helps to stand up on the pedals and shift position frequently.