Difference between these sticks?

[Deific]

Could someone please explain the difference between these two sets of memory to me?

I know ones at 1.65v with faster timings and the other at 1.8v, but why are the sticks with faster timings cheaper and what are the implications of the voltage difference?

http://www.overclockers.co.uk/showproduct.php?prodid=MY-193-CS&groupid=701&catid=8&subcat=1517

http://www.overclockers.co.uk/showproduct.php?prodid=MY-197-CS&groupid=701&catid=8&subcat=1517

 

[Deific]

good to know, but that answered none of my questions