Excessive stuttering and occasional FPS drops in Optifine-enhanced Minecraft 1.7.5 despite high framerate [closed]

I am playing Minecraft 1.7.5 with Optifine on high settings (all video settings except OpenGL set at fancy). I get a consistently high framerate on average: 90-140 FPS. However, I also experience constant stuttering, and occasionally even massive framerate drops that at their height bring the FPS down to even 20. Also, the VSync does not work.

The PC specs are:

2.6 GHz Dual-Core Pentium;
3.12 GB RAM; Nvidia GT 610 Video Card

How much ram do you have, and how much allocated to Minecraft? You might want to bump that up a bit. If you do not have a lot of ram close some programs or buy more. Maybe also upgrade from a old and slow HDD to an SDD. Or just buy a whole new computer. I mean, who even uses dual core processors anymore these days? (except for grandma)