1024 + 512 = 1536 - 64 = 1472
Maybe I'm not adding it right but i should be close.
Either way if the system is running faster then we should have the original issue resolved.
Have you tried to play a video now to see if it is still choppy?
I have 2 gigs of memory and depending on where I go to watch a video it will still be choppy.
Buffering along with bandwidth will affect the video.