4GB > 3GB In MacBook C2D

I upgraded to 4GB today, bought a 2GB stick for only 30 bucks w/ tax and shipping and all that. The upgrade was quick and painless but I noticed a MASSIVE increase in speed. I was running 3GB before and I noticed a bit of slowdown. Granted, I did dedicate 1GB of Ram to Parallels running Windows Vista. Right now, after my upgrade, it reads 4GB but I'm pretty sure it only uses 3.3GB, the speed is incredible. Nothing lags, I boot into OSX from Pressing the button to logon screen in 6 Seconds today.

Could this be the 128-bit thing people were talking about? I'm not completely sure.

I have the older one. The one I have is the Black 2.0GHz Model, Non-SR. It was officially rated for 2GB, but I upgraded to 3.. then to 4. Leopard says I have 4GB, because I physically have 4GB, but in the activity monitor, it only adds upto ~3.3GB more or less.

My primary use is Virtual Machines, but I do, do photoshop work, run excessive amounts of programs at once (mail, ical, firefox w/ 20 or so tabs, itunes, adium, bonic, parallels, ichat.. just to name a few) From 1GB to 2GB, everything was a lot smoother, but there was still a slight lag, especially in stacks. From 2GB to 3GB, it was better for the virtual machine, but the system lagged more then 2GB because I lost Dual Channel. Some parts, especially the animation, lagged on the 3GB (such as stacks opening up). Here at 4GB, everything runs butter smooth, literally. I usually run 1 or 2 Virtual machines at once, depending on what machines (like linux and windows or 2x linux, etc) and even with the VM running some type of background program, stacks don't lag or opening any other programs.

From what I've seen, if you have 2GB, its better to stick with 2GB or upgrade to 4GB, skipping 3GB in between. Obviously more ram = a little faster, but you lose dual channel which somewhat kills the performance boost. But you get more ram, so thats a good thing.