I have always been able to load Minecraft (with Optifine) on 512x512 resource packs with no problems until today. I have not changed any hardware or software, and I have tried various different parameters. By default I have 8 GB of RAM allocated to Minecraft. I am running on the latest stable version of Optifine Ultra in Minecraft 1.7.4. All drivers are up-to-date, along with Java 64-bit (7u51). Now, once I try to switch over to the x512 resource packs, the game stalls with one of my CPU threads maxed out at 100% (totaling roughly 13% across the entire CPU) until I manually end the process. When I changed all of Optifine's video settings to the absolute minimum and tested it again, it would stall and max out a CPU thread for about fifteen seconds, and then revert back to the default resource pack. From what I've read, that means I ran out of VRAM, which is confusing because I could run it before. I have tried re-downloading the resource packs and Minecraft itself to no avail. My computer's specifications are as follows:
CPU: Intel Core i7 3770K (3.5 GHz, Not Overclocked, 4 Physical Cores, 8 Logical Threads)
RAM: G-Skill Sniper Series 16 GB DDR3 1600 MHz (Dual Channel)
MOBO: MSi Z77A-G41
GPU: AMD Radeon HD 5870 (1 GB VRAM, Not Overclocked, 850 MHz Core Clock, 1.2 GHz Memory Clock)
HDD: SATA 2 TB (7,200 RPM, 6 Gbps)
Monitor: 21.5" Dell ST-2310 (1920x1080, 60 Hz, 32 bpp)
OS: Windows 7 Ultimate 64-Bit
Average Idle Usage: <1% CPU, 10 KBps HDD, <1% GPU, <1% VRAM, <10% RAM, <30 Processes, <1KBps Net
Any information you can give to help me solve this problem would be greatly appreciated. Thank you in advance!