Mongo-perf includes "comparison variants" to compare the results of the wt variant vs the mmapv1 variant. These were used in 3.2 release, where the requirement was that wt must be faster than mmap.
After discussion, we agree that these variants have now served their purpose. (And have caught little to no regressions anyway.) As WT has its own performance history now, it is more useful and less noisy to simply compare WT against its own history.