Ever since the new launcher has been released, I've been getting FPS that has been ranging from 25-10, which I normally, I get 70+. This FPS drop affects any version of Minecraft I play.
I believe it's the new launcher because I created a profile with 1.5.2 and compared the results, same position with all the chunks loaded. The new launcher has a large FPS drop.
I do have mods installed, but the exact same mods are installed to both clients, so mods are most likely not the reason. Mods Installed: Too Many Items and Rei's Minimap.
Force Crash for both launchers included. If any more information is needed, I will try to supply it.