• Remove all of the garbage Voxel aesthetic mods (menu, loader, map)
• Use optifine and (if you want fancy textures for everything else) set tree leaves to Fast (especially in EXBL biomes)
• Use less RP circuits (they're horribly laggy, especially timers)
• Use jacketed red alloy wire over uncovered red alloy wire
• If it's possible, use vanilla redstone (no need to go up walls etc)
• Use TE Liquiducts over BC pipes
• Don't use Mekanism ANYTHING (the lag is abysmal)
• Prefer TE igneous over BB/Timer combo cobblegens
• No XyCraft blocks.. or the mod.
• No Crystal Chests
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The two most computer and server friendly (big) mods are Thermal Expansion and, believe it or not, Gregtech.
Redpower is the destroyer of framerates.