PC Wizard has the following to say about the voltage and timing of my ram now:
Voltage : SSTL 1.8v
CAS Latency (tCL) : 4 clocks @333 MHz, 5 clocks @400 MHz
RAS to CAS (tRCD) : 5 clocks @333 MHz, 5 clocks @400 MHz
RAS Precharge (tRP) : 5 clocks @333 MHz, 5 clocks @400 MHz
Cycle Time (tRAS) ...