Bigger, Faster...Stronger? - Memory question

[Megalo]

Is it better to have 20GB at 533Ghz Memory or 16GB at 677Ghz Memory? I have a machine that I put 4 x 4GB of new memory (Dell T3500). Then new clock speed for the new memory is 667Ghz. Since there were two more slots, I put 2 x 2GB old sticks back in for a total of 20. The old sticks are 533Ghz. Do the old sticks slow the other modules down to 533? Would it be better to have 16GB of 667 instead?

 

[C12Friedman]

Welcome to Tom's Hardware Forums,

Do the old sticks slow the other modules down to 533? Would it be better to have 16GB of 667 instead?

Yes and yes

 

[Majestic One]

take out the 2's and maybe play with over volting if you wanna OC.