Looking at SiSoft Sandra, we can see that we've got some strong memory performance coming out of the Maximus IV Extreme.
Replacing Everest in our labs is AIDA64. This new testing suite is from the core development team from Lavalys and continues that tradition. The guys have thrown in better support for multithreaded CPUs as well as full 64 bit support. We use this to test memory and HDDs for now, but may find ourselves opening this up to other areas of the motherboard.
Looking at AIDA64, memory performance is strong that of course becomes even stronger when we overclock our CPU which helps offer even more bandwidth even though our actual memory speed changes only a little.