xpleet, the /3GB switch allocates more memory to the applications, removing it from the system (kernel is reduced to 1GB max). The /PAE switch gives more memory back to the system. This is only relevant for servers, like terminal services and similar. I think you do not need the /PAE switch and it could be working against you.
Another thing is the /userva=3030 fix. Actually, I remember reading that Microsoft does not recommend going above 2090 here.
I'm not 100% sure about the things above. I never tested it myself, I just know it theoretically.

Another thing: did you increase your pagefile accordingly? If you have more physical RAM now, you should increase the pagefile also. The rule of thumb says it should be 1.5x the size of physical RAM but that's for low values of physical RAM. For 4GB you can probably just have 4GB. The right way to calculate it is complicated though, but there are several sites which can help you. Just google for "pagefile size".

Regarding Vista 64 and its alleged problems, all I can say is that I have it for several months and I'm very happy with it. It runs smoothly, fast, no problems at all.