The GP's are only average in rolling resistance unlike what many will say.

Here is one report, the GP Attack and Force tires are very similar to the GP4000: http://ddata.over-blog.com/xxxyyy/0/...her-specs.html

Just in case that one is not good enough there's this one: http://www.biketechreview.com/tires_...sting_rev9.pdf
Note on this review that some of the test are done with latex tubes which improves the performance of the rolling resistance tests.