Is that 1600ht accurate?

AT the moment I'm just playing about with overclocking, the HT frequency option in the DFI fxb-m2rsh board doesn't seem to be altering anything unless cpu-z isn't reporting it in windows 7 64bit. Though its tracking nb speed and core clock fine at the moment. Is there any trick to changing the ht frequency without raising the bus, some option in the bios that needs to be set?

3.6Ghz was a breeze but 3.8Ghz would get iffy getting into windows, mostly not making it. Is it still the case you really need the HT at over half your core speed and equal to or less than northbridge clock?