Why Does FTB on Minecraft lag so bad?

I can play Attack of the B-Team and Tekkit with over 30 FPS on normal settings and they each have 100+ Mods. FTB unstable only has 24 mods and on medium settings I get about 10 FPS. All the FTB modpacks lag so bad, but technic ones run fine.

Added (1). Oh yea, I put 3GB of memory on each one too, that's not the problem.

Zachary Swanson

Sum parts of the mods may have more content or stress the graphics card/processor etc.
Try derping around in the setting until you find it in a playable state.

Kaleb