I will be purchasing a Mac Pro tomorrow. I ordered 4GB of RAM from a highly accredited third party that several other people I know have used with no issues, anyway. My question is should I put this RAM in before I start up the machine for the first time, or let it run the initial startup sequence then power down and install the RAM and restart, or does it matter?
I would test it without upgrading it first. Then shut it down and install the ram it only takes a few minutes. I would buy another 2 512Mb and install them in slots a&b of board 2 with your 4x1Gb in slots c&d of boards 1&2. This is what I did. You will get a noticeable increase in speed due to having 2 banks of 4 identical fb dimms. The cost of 2x512Mb is very little for the increase you will get. There are plenty of articles in relation to this on the internet. If you do not want to buy the extra 2x512Mb to begin with try the 4x1Gb in slots a&b of board 1&2 and remove the 2x512Mb completely.
The mac runs quickest with FULL sets of 4 fb dimms in slots a&b of both boards. There is a slight latency hit if you have 2 sets of 4 ie all 8 slots used but this hit is only 3-5% and will be USUALLY made up for with the extra memory. The performance hit of having incomplete sets of 4 has been shown to be 15-20% in certain tests.
If 4Gb is enough for you try if without the 2x512 to begin with. I, like you, bought the 2x512Mb and bought 4x1Gb from kingston but having read the reports also got the 2x512. I had the 512s in board 1 and the 1Gbs in board 2. Just setting it up correctly with them spread across the 2 boards like I explained earlier gave me a noticeable improvement.
Hope this helps. The questions over Mac pro ram come up every week maybe I should just do an indepth article and post a link!