For optimal performance on machines using an Intel processor, I can recommend the following setup for maximum performance on 1.7.10:
Install FastCraft.
http://forum.industrial-craft.net/index.php?page=Thread&threadID=10820 There is absolutely no reason not to have this, most modpacks are smart enough to include it now.
MultiMC 5.
http://multimc.org/ Beats any other launcher in terms of speed, flexibility, and support. You can manually import packs from other launchers and it has support for automatic launching of FTB packs that you have downloaded.
Minimum memory allocation of 256MB. Java is mostly grown up, it can decide how little memory it needs. Realistically your minimum will sit closer to 512MB but that's okay.
Maximum memory allocation of 3072MB. Most packs are just fine with this much, the less memory you can allocate, the better garbage collection performance will be. Experiment to see how low you can go, I find 2.5GB is enough for my custom pack.
Java 8 Update 45 Development Kit. Better known as JDK, you can find it here:
http://www.oracle.com/technetwork/java/javase/downloads/jdk8-downloads-2133151.html Make sure the launcher is set to use that specifically if you have other versions installed.
Leave the PermGen alone. Java 8 handles this independently and its called MetaSpace, which you shouldn't touch. Set it to 256MB if you ignored my advice and used an outdated version of Java.
Make sure your
power plan is on High Performance. Some computers default to the Balanced Plan which usually hampers your graphics card performance at minimum and your processor maximum speed in some cases.
Still having performance issues? You either have insufficient hardware or a mod causing problems. Below are some solutions you can try:
Get Optifine HD U B5.
http://optifine.net/downloads.php It has some minor overlap with FastCraft but does provide another performance boost, it does occasionally introduce a rendering glitch though.
Add -XX:+DisableExplicitGC to your client JVM arguments. This rarely fixes anything because modders shouldn't be stupid enough to manually invoke garbage collection. If they are, this stops them from doing so.
Run the game at lower resolution. This only helps if you are limited by your graphics card, this would only be the case with weak graphics processing units, such as those integrated into processors.
Switch to or dual boot a Linux kernel based operating system. This will have the largest benefit if you are memory limited, it saves a bit of memory and you can disable all the stuff you don't need. Avoid this option if you are also graphics performance limited, as the graphics drivers are usually best on Windows. I suggest something Debian based like Mint or Ubuntu if you are new to Linux or Arch Linux if you are adept and don't mind a learning curve.
That's all I have for now folks. The list is in order of measurable effort, from smallest to largest. Shoot me a message if there is something I should add to this list.