I was thinking the same thing. For the price of memory I plan to max out my system.
It's not only RAM that's necessary, also your processor and video card matter. I have a laptop with a GT 540M graphics card with 2GB dedicated to it, then another 6gb for the system and a i7 processor and even with this -quite good- set-up it sometimes goes slow with HD, so maybe you should consider using/ buying a better pc.
And Sony Vegas will indeed be better