Done Reducing Fps lag

I have researched a bit about your CPU, and its a bit meh..... :/
Because it has a maximum Clock speed of 2Ghz. So i hope you have on other modpacks somewhat like FastCraft or Optifine, but as you said with optifine you get from 2 to 6 fps. Which is still and improvement. But let us be honest you cant play like that.

Maybe try FastCraft, dont know about the mod but i know it helped some people out.

What i think the problem is, is that Regrowth doesn't have any mod that gives you multi-core support to get most out of your CPU.
So what minecraft does it uses only 1Core of your CPU, like most of the games do, and all the power on other cores is not used.

And a tip i would not give minecraft more than 2.5gb of ram, that's actually the limit, 2gb should be fine, because you need ram for your system to run smoothly.

If someone thinks im wrong. Feel free to correct me

Could you do the same thing and find out the CPU of your Mom's Laptop?

P.S. Newer doesn't always mean better

 

permgen should not need to go over 512, and you cant allocate the entire 4GB ram since the average OS uses at least 1 on its own to run correctly. try the min ram as 512mb max at 2gb. Then try opening your resource monitor while running the program and see if maybe it is forcing several Java JRE applications to run (happens when you have 64bit & 32bit at the same time some times.)

the next suggestion is maybe remove the mods that are not needed from the pack (ex. tabbychat) and see if reducing the strain helps, if it does then there you go. If not then try doing some system clean up, perhaps your temp files are being accessed for some reason.

 

Have you tried optifine, i've noticed that this pack contains a bit of particles that may cause FPS drops. Mostly Botania (Mana Spreaders, Rods, Flugel Wings, Weapons, etc) lowering down the particles might help out.

 

Check if you have advanced openGL enabled, can you post a screenshot of your video settings in minecraft?