I dont know if Im to late for you now but I went from a athlon xp 2500 to a athlon 64 x2 4400, 2GB dual channel ram. I thought I would have seen more of a difference, since it was a 4 year old cpu & system. It is of course faster but not what I was expecting. Maybe I got 30-40% faster. I might trade to a faster cpu in a few months and maybe then Ill be at double the speed from before. Im just guessing but a movie that took my old computer maybe 10 hours to put together takes 6 now. So what was an all day project will now be an all morning project.
I believe the intel cpus are faster, but they cost more, so like always the faster you want the more you pay.