I was at 1x warp 10 seconds before hitting the line I like to celebrate it when i get those survey ships out of orbit since their such a pain to haul up into space.
TiberDyne has a really good cargo door for the MK3, it's one of my favorite parts, only issue with it is that it doesn't allow you to attach wings or anything to the outside.
You may want to add the RSD-100 Range Safety Device to your list of not usable mods, otherwise this challenge is a cakewalk. http://kerbalspaceprogram.com/forum/index.php?topic=5660.msg72838#msg72838
It's overheating. There's a glitch that makes it on some rockets not show the overheat status. Don't burn it as hot and you'll make it all the way to the end of the run.