I have 99 mods installed, and the only "global" ones is Biomes O'Plenty and maybe Nethercraft, other mods only change/add a few things.
Every time I break a block it doesn't break instantly. The time that has to pass before it breaks is the same as the time needed to break it*2. (For example, when I break a block that takes 0.5 seconds to break, I need to wait 1 second before it is really broken)
And, every time the world loads, there's even more lag. Even videos I have open in the browser (Google Chrome) pause for a second. I guess the problem here is my C drive, but it was cleaned recently, and now it has almost 20 gigabytes free.