thats because its the same core and stepping as the 4400+ so u wont get as good results as someone who saved money by buying the 4400+ and over clocking it to 2.5-2.6, Your chip just has a higher multiplyer on it, nothing else is different.
Well, you are already water cooled so there goes my first suggestion. You are probably very close to the max for this processor. Few of those athlons 64's much less the x2's are doing over 2.7 ghz.