Next Upgrade?

First Post! My system was built one year ago today. Reading advice in this forum allowed me to build the system even though I had zero experience. It runs great, but the itch is there to do something more.

Vista Ultimate 64 bit, Intel Core2 Duo 6300 @ 3.0 GHz w/ Scythe Ninja, Asus PB5 Deluxe Wi-Fi 1226 Bios, Silverstone ST50EF-Plus 500Watt, Antec P180B with 6 Yate Loon 120mm fans at 600 rpm + AcoustiPack foam, nVidia 7900 GS w/Thermalright HR03, Corsair 2GB XMS2-5400, WD RE2 500GB w/ 16MB, WD Raptor ADFD 74GB w/16MB, Samsung S182D DVD, Mitsumi FA404M

I run general applications, using this for my business running mostly Excel models. I also do a bunch of video encoding, but no gaming. I generally have 5 to 8 applciations running at any time. My primarily desires are to increase the speed of applications loading also the snap of moving between applications, cutting and pasting data etc. Video encoding is in the background, and it takes what ever it takes, but it does occassionaly bog everything down. I have done what I can to optimize the software with virus, defrag, indexing done during off hours and turning off some Vista 'features'.

Question 1: Will additional RAM memory (so cheap now) provide a noticeable gain. Unless I am encoding video my 2 GB of RAM seems to remain at a steady 75% utilization. What speed should I look for, and I suppose I should look to get 2GB sticks. If I do so what should I do with my existing memory?

Question 2: My 6300 can be overclocked a bit more to 3.4 GHz but that is about it. I was considering upgrading the CPU to either E8400 and overclocking, or Q8200 which are roughly the same price. Will either give me a noticeable real world speed jump, which one more so? Does this impact my ram decision or can I stick with what I have.

Question 3: Will overclocking the GPU speed up my video encoding (I primarily use VideoReDo and DVDFab5)

Thanks, Bear 100