Try:
Craftguide in place of nei.
Exclude:
Extra utilities, open blocks and other mods that add lots of random items as they load memory with unused textures and code. Redundancy is the enemy in low spec packs, so choose ONE mod to provide RF / ore doubling.
BOP and other biome adding mods as they use a lot of texture memory.
Also:
The barrels mod for barrels vs jabba / factorization.
Use AE in place of TE3/BC pipes for automation.
Ruins. Infernal mobs for adding content without new textures.
Measure your success:
In part, in game, by hitting F3 and seeing the java memory used / Available. On low spec packs I stop adding mods when the memory used starts exceeding 520Mb.
There are no good tools for determining texture memory load, short of watching your MC logs for OpenGL errors.
Ignore my advice and:
Add Twilight Forest. For the huge amount of content. It doesn't add anything to the overworld so your overworld fps should not be effected by having it available.
Dedicated Server:
By running a dedicated server you split the requirements for MC between two OS processes. You could even run the server on a separate PC. The server will handle world gen type tasks and mob AI and the client will handle the texture memory pressure. Especially on 32bit OS's where processes have limited virtual memory available this can help larger packs work on lower spec hardware.
--
My 1.7.2 modpack looks like this. It is for SMP play, so expects perhaps a beefy server, but tries to keep the client load down:
Magic:
Thaumcraft & Blood Magic.
Tech:
Applied Energistics 2, hopper ducts mod, the barrels mod, Ender IO
Content:
Infernal Mobs, Twilight Forest, Ruins, Doomlike Dungeons, Rogue-like Dungeons, Mystcraft.
Decorative:
Mr Crayfish's Furniture Mod, Bibliocraft.
It, purposely, does NOT include automated mining or automated farming (outside of thaumcraft), as we wanted to emphasis world exploration over complicated tech builds.
I am unhappy with:
Bibliocraft for having high rez models. But its bookshelves and armor stands are too nice to loose.
Mr Crayfish's Furniture Mod: Minebay and the Printer are unbalanced, but its decorative items are too nice to pass up.
EnderIO - has added a one block auto crop farm and powered mob farms. Unwanted, but without TE3 I was stuck for RF (to power AE2). Plus its solar panels provide passive RF which is sorely needed without quarries / heavy auto-tree/crop-farm mods providing (laggy) infinite power.