My Mac pro came with 2 x512mb modules and i purchased 2x 2gb modules from OWC. I placed the large modules in the first two slots of riser A and the two 512mb's in the first two of riser B. I'm presuming this is correct as i don't see how better to configure them?

I was looking at some test results for the Maco Pro using raid. Just one extra drive made a big difference. This machine has the Seagate Barracuda drive, this one i presume

So i'm thinking of buying another for a raid setup. Worth sticking with these drives or just purchase another brand and model? Thanks.