Memtest 86 lower memory scores with more speed?

Well i got my new mobile 2500+ today and while testing for some stability before going into windows i used memtest 86. Well for some odd reason the memory speed kept going up from 2300 mhz @ 855 MB/s to 2500 mhz @ 912 MB/s but after that it started going down to like 876 MB/s while being @ 2600 mhz. I'm assuming errors started from the cpu but its just a wild guess. Specs in sig. FYI i'm running @ 2500 mhz ATM @ 1.8 volts. Still testing as we speak! =D