If the web site states 1.8v for 800 Mhz memory, I think there is a typo.
To my knowledge (someone correct me please)
DDR2 by spec is supposed to run at 1.8v
The only silicon available that runs at 1.8v is 667 Mhz (micron DG9 xx chips are a prime example)
Every memory manufacturer overclocks the memory to get the rated speed
to get 800Mhz 1.9 is good, some (like corsair specify 2.+)
Virtually all of DDR2 memory is the same 667 Mhz overclocked to a different level. The most that has been done is around 1250 / 1300 Mhz. Corsair XMS2 PC 10000 (1250 Mhz) is set to run at whopping 2.4 volts and comes with a cooler as internally it still runs 667 Mhz silicon.
The point is - I'm yet to see the chips that will clock 800 mhz at 1.8v.