Hi there, did you ever find the solution to this?
I just created this http://www.reddit.com/r/dogemining/comments/1x04jq/just_got_a_second_gpu_which_is_100_identical_to/, and it seems like we have the exact same issue. I too have 2x 280x vapor-x, both of mine are running at 99% load though.. But one of them is mining less but still gets hotter.