Yes, I understand you perfectly, it seems that this issue arises only when you are at the border of filling your gfx card, the file is 128*something, so this size indicator is somewhat faulty. I tested it with only optifine and forge, and by my understanding of the compatibility(which is in place, since my friend is able to run this combination, she does have more memory as well), but it seems that hd textures when run in conjuncture with optifine AND forge overload the GFX memory much more. By taking a wild guess I'd have to say that some textures are loaded twice due to how forge works and how optifine works. And I know that you do not support this officially, but I wrote to the optifine creator and wanted to hear your opinion as well. If you have any additional ideas, throw them at me.
Thanks for the reply tho.