Hi,
I had almost the same problem with the same error (EXCEPTION_ACCESS_VIOLATION (0xc0000005) at pc= ...) the game would close after a few minutes of play. I tried using Optifine Ultra D5 and the normal D5 also had ruins and enchanting plus installed. The client had 12gb memory and ran with high priority.
I fixed my problem by disabling the Voxel-mods.
After some testing it seems that only the Voxel player was to blame. It runs fine now with the others enabled (core, map, etc).
Hope this helps you!
Also search this forum for the error there are 2 posts about it, that might help you.
GL!
Doel