It can definitely vary. Have you been riding a lot in the Texas heat? Some have suggested heat training helps with altitude since there may be some overlap in the adaptions such as increased plasma volume and hematocrit. With Leadville being cool, you may have benefitted from the cooler temps and then not been hit quite as hard by the altitude.
Coming nine nights before and staying at altitude will help. My own experience is that after 7 days I feel the altitude a lot less. Team Sky reported in the past that 7 day altitude camps were ideal for their riders.
Given the length of Leadville, you might want to shoot for 0.7 IF during the first half. If your FTP is accurate, I think 0.75 in the first half might be a little risky. After Columbine, if you are feeling great, then you can start to push a little harder knowing you are in the back half. The big test is Powerline at Mile 80. On race day this is probably the biggest challenge on the course. If you feel good after that, you are golden and can drop the hammer until the finish.