Mixing DDR3-1066 and DDR3-1600 RAM modules- question!

[allfiredup]

A friend asked me a question earlier tonight about mixing different speed RAM modules on his new laptop....

The laptop came with a single 4GB DDR3-1600 RAM installed in one slot and the other slot empty. He has a 4GB DDR3-1066 module that he would like to install for a total of 8GB of RAM.

I know that you can mix RAM of different speeds and I confirmed it by installing both in his system. I also know that the system downclocks all memory to the speed of the lowest. So I'm assuming that all 8GB are operating at 1066MHz. Before I added the second module, the original 4GB was operating at 1600MHz. Right?

So, here is my main question- Even though there is a slight difference in memory speeds, the 8GB at 1066 will outperform the original 4GB at 1600. Am I correct? Would it be worth it to purchase another 4GB DDR3-1600 module and toss the DDR3-1066?

Please advise, thanks!

[MidnightSun]

Yes, the RAM is now running at 1066MHz. No, you won't be able to notice the difference at all unless you use the integrated graphics for gaming purposes: then, the faster RAM speed will benefit overall graphics performance and 1600MHz versus 1066MHz may net you a couple frames per second difference (under 10 FPS).