general memory bandwidth question

I was under the assumption that for example if i bought DDR2 PC2 8500 put it in and set the timings to 4-4-4-12 @ pc2 6400 speed.. that it would be exactly the same speed as if i bought ddr2 pc2 6400 it in and ran it at 4-4-4-12 @ pc6400 speed....

i have a few sticks of both and recently i was hunting down a memory problem.. and ran memtest a few times with both types of sticks in the computer seperately and for some reason with the speeds set identical memtest was reporting almost a 1000mb/s increase versus the 6400 sticks..

I don't understand.

Either they werent running at the same speeds like you thought, or the sub timings were set differently. Something has to be different as your first assumption is correct all other things being equal.