It also depends on what you want to display in which resolution on an external display.
3D applications like Maya (and other GPU intensive applications) might not really like being put through an Intel HD 3000 onto an external 2560 x 1600 pixel display, but having Word or Safari display a window on that same external display is not really a problem.
Anyway, since TB is not really the problem, but the GPU, what has your thread title to do with your post again?