Need help adding more DDR2 memory

I currently am using 2 of my 4 memory slots on my motherboard. I have 2 - 1gb sticks of OCZ PC6400. I am looking to get 2 more sticks of OCZ for the other 2 slots ,BUT am not sure if I get 2-512mb sticks will they perform well with the 1 gb sticks??? Or should I get 2 more 1 gb sticks so all 4 sticks are similar???? Sure hope this makes sense,,,

as long as the 2x512mb sticks are matching, it should work fine, giving you 3gb total.

keep in mind, some platforms or mobo's don't overclock so nice with 4 sticks of ram. i would try to ask ppl with the same board or similar if they have any experience there.

Im not sure if I should post this under memory or motherboard ? I know that the 512mb would work with the 1gb sticks, Im just not sure if I would get better performance with 4 matching 1gb sticks

I'm not sure that it's any performance you will notice. Although, having 4GB over 3GB would probably be better with Vista.