I have a Vista 64 bit set-up. I have 2GBs (2 sticks X 1GB) and have added another 4GBs (2 sticks x 2GB each) - grand total of 6GBs.
Both sets are Gskill DDR2 6400 (800mhz)... but the timings on the 1GB sticks are tighter 4-4-4-12 vs. 5-5-5-15 on the 4gb upgrade (wasn't paying attention when I jumped on the deal). I think my MOBO defaults it to 5-5-5-15 anyway (Giga P965 DS3 rev 3.3).
My thought was that keeping the 1GBs sticks in the primary slots would make programs run faster, but maybe the system would run better with a larger "pipeline" in the main slots. This would reserve the 1GBs for overflow.
Heavy gaming and photoshop usage.
PS- I feel like such a man now, Visa is only using 23% of my ram (as opposed to 50%).
the different sets will NOT run at different latencies. So youll find all 4 sticks will run at 5-5-5-15 unless you want to try and tighen this. So it will make no difference what slots they are in. Just make sure that both 1gb's are in one dual channel pairing and the 2gb's are in the other dual channel pairing. If you mix a 1gb stick with a 2gb stick "dual channel" wont work.