the basic difference in the ram is this
one works at a higher frequency that the other ie one can run at 800mhz while the other can only run at 667.
afaik this only makes a diff with the kind of processor you have
if u have some processor running at 667mhz no point in buying ram running at 800mhz
cause then the ram will also be working only at 667
btw in your case both of those processors are over 1k Mhz so i guess it would be better to go with the 667Mhz..
all of the above are just my views..
im so gonna follow this to see what some expert has to has about this