Matching RAM speeds

My system currently has 2GB (2x1GB) dual channel PC5400 (667) RAM installed.

After looking at Scan today, always a bad idea as its so easy to be tempted, it appears that the price of RAM has crashed.

So what im asking is can i fill the other dual channel slots on the motherboard with a higher speed RAM (eg PC2-6400 (800)?

Is this acutally worth while or am i better to save a couple quid and go for the slightly slower pair and keep it all matching?

Hope its not a really obvious question, its just something ive been wondering.

It's a bad idea, always run matching RAM for system stability.

Of course you could set all dimms to run at set speed / timings via the bios, but there are internal latency timings of the sticks.

Thanks,

I did think it was probably a good idea to keep it all matching, but thanks for confirming it.