Running the client on its own gives me a butter smooth 60fps but becomes choppy when I run the server. The impact on the fps seems to be only a few frames according to the debugger leading me to believe this is microstutter. I have 6gb of ram dedicated to my client and 2gb dedicated to the server. Minecraft version is 1.7.2.
Specs:
3.40 gigahertz Intel Core i7-3770
12gb RAM
NVIDIA GeForce GTX 660 Ti