What reason do you have to believe they are one step colder? Why wouldn't you say one step hotter? You're begging the question...
Check out the first picture in this thread:
http://www.e90post.com/forums/showthread.php?t=695797
The BMW plug's box even says ZGR6STE2! I don't know what more proof anyone could want or expect.
They're stocked at Amazon with the same PN listed:
http://www.amazon.com/Piece-Bosch-Spark-0242140507-ZGR6STE2/dp/B00804F080