Quote from MechJunky
What really irks me is when I try to combine super shaders with 216x216 texturepacks. I know my computer can handle it, but in task manager the memory is staying at 30% consumption. I have 8gb, which during this time minecraft is lagging up the butt. How would I give it more memory?
Did you try looking at your CPU and Graphics usage? EvilCreeper is right; Minecraft should never really use more than one, or in extreme circumstances, two gigs of ram.
Shaders are usually a graphics card thing, so your graphics card might not be able to handle the shaders very well.