Mixed up RAM!

[Octavarium]

I'm wondering whether or not my current RAM is likely to be causing probems...

I have 2 sticks of OCZ 256mb (Dual Channel) from when I bought the PC and have since added a stick of Samsung 512 and then an unbranded 1gig stick.

Each time I have added more RAM the PC has become noticeably faster, but upon adding the last stick (1 gig unbranded) it has become a touch more unstable.

I guess my question is whether or not having such a mixed bunch of memory is likely to cause problems?

 

[Octavarium]

I must admit that I don't even know how to adjust timings!!

I'm starting to think its best to sell it all off and replace it with a pair of matched 1gig sticks.