Memory question

Hi all,
I have 2 sticks of PQI 2x512 that I am happy with..
http://www.newegg.com/Product/Product.asp?item=N82E16820141152
I want to add 2 more 512 sticks,but I remember not to long ago for overclocking in dual channel using more than 2 sticks didn't work to well.
Question I am asking should I get two of the same of what I got to use all 4 slots?
Or should I get 2-1 gig sticks?

Thanks

It won't work "well" if well equals the performance of a single set. However, you can loosen the command rate to 2T and probably get upto 85% of your previous OC. A lot depends on how well your sticks are matched. Don't be afraid to switch sticks around for optimal performance.

Thanks for the quick info
I guess the same would be true if I decided to get the 2X1 gig sticks and used them along with the 2X512 sticks??