With render distance on short, no clouds, optifine, got my highest ever fps at an incredible 15!!! Yeah, my computer has no graphics card and piggybacks off of the processor which isn't that great. That's why i'm saving up for a new laptop so I can get at least 25 fps (super uber fast)
ANOTHER EDIT: I loaded up Minecraft, turned all settings down, put on the default texture pack, lowered the FOV to Normal, and loaded up a superflat, peaceful, (so no slimes) no structures, world. Checked FPS with F3, 1012, without any mods whatsoever.
Turn down all graphic settings tot he lowest. Stand on the bottom layer of the world in a flat creative mode world in a 1x1x2 hole and look down onto a solid stone block. Watch fps skyrocket into the thousands without mods.
F**k my pc. I get about 40-60 fps with normal render distance all settings up and optifine -.-! FUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUU RAGEEEEEEEEEE NOVA MODEEEEEEEEEEEEE ARGGGGGGGG