Trying to run Sphax PureBDCraft 512x

[KingOfParsnips]

Ok. I know you guys probably see this often but I'd like some help in trying to run Sphax 512x on Minecraft. Before I get started these are my PC Specs!

Nvidia GeForce GTX 970
8GB DDR3 1600MHz
Intel Core i5-4690 3.50Ghz
Seagate Barracuda 2TB 7200RPM Hard drive (If this is necessary?)

Just a guideline Im running about 350-500 fps with Sphax 256x

I'm not sure if I added RAM correctly but in the top corner after pressing F3 Ingame it says:
Mem: (Random number)% (ram usage)/3788mb
Allocated: 91% 3462MB

With this amount of RAM allocated Minecraft just attempts to load it for around 2 minutes and then load basic MC textures? With less RAM Minecraft just crashes? Anyone know how to fix this?

[HanFox]

If this is for MC1.8 it's been widely stated you need to allocate 16GB+ and that it generally works better on Linux.

I'm aware that doesn't make any sense considering you can use 256x just fine, but that's just how it works because Mojang somehow messed something up.