Advice on mixing 2 speeds of RAM

[frasier]

ok, I currently have 2x256 3200 RAM,

I'm getting 2x512 4200 RAM

would it be better to

A. mix those and get 1.5gb of ram @ 3200
or
B. Have 1gb of RAM @ 4200

I need an answer quickly, please

 

[sllewe]

Dont mix...it could work, but more then likely your gonna have problems. And 1gb should be efficent. WIth the extra sticks you cant use dual channel.

 

[Tedster]

memory will only run as fast as the slowest one. In a nutshell - don't