According to every source I read in a short time about it, NBA 2K11 lags cause of the priority settings. So you should set the priority to high. Hope it helps, thank the genius of Google if it does.
I have an i7 processor and I was having the same problem with 2k11, what fixed the problem for me was disabling a couple of my cores. While you're playing 2k11 hit alt+tab. Go to your task manager and find 2k11, then un check a couple of your cores. That worked for me.