Pollock,
I recently saw an A64 overclocking article that used a dozen or more benchmarks to correlate overall system speed to memory speed, memory latency, and cpu speed. Their conclusion was that increasing memory speed or reducing memory latency alone had a measurable but limited impact on system speed, however increasing A64 cpu speed was effective even when not matched by an increase in memory speed.
They suggest that it's due to the memory controller being on the cpu die, so overclocking the cpu is unusually effective on overall system performance with A64s.
So a cpu overclock in an Athlon 64 system may give you positive results even if you have to slow down the memory a bit. You'll just have to give it a shot and see if it helps in the apps you run. Knowing that AH2 seems to be mostly cpu limited, I think it may help.
If you really want to overclock your memory too, memory sticks that use "TCCD" chips seem to be the ones to get. Many manufacturers sell these under several brands. OCZ brand memory seems to be high quality but they cost a lot. "OCZ EL Platinum Rev 2" is supposedly one of the better ones, but as I went with crucial ballistix memory that uses different chips, I haven't kept up with what brands use TCCD chips.